How to make print-ready PDFs

Here are the few but necessary things you need to know to turn a beautiful design into a beautiful print without pre-print having to replace the designer's work when handing the executive to the printer.

By Lorenzo Capitani | On PRINTlovers 98

It has now become standard practice for prepress to intervene to correct errors in executives such as missing abundances, low resolutions, lack of profiles, unintended colours, non-printable fonts, and 4-colour black text. But prepress should operate for printing: normalise PDFs, do the cyanometrics and start the job in print after the visa print. Once upon a time, between the artistic and production phases, there was the photolithographer who consolidated the layouts and produced correct executives for printing, then increasingly accessible software, digitised processes and cost-cutting have shortened the chain, internalising a series of operations with the illusion that everyone can do everything, even without adequate technical knowledge. And so printers have ended up making a virtue of necessity, preferring to intervene rather than send the job back to the customer with the risk of explaining the problem and perhaps how to solve it.

Yet there are not many things to pay attention to, nor are they so difficult, but they are crucial to turning a beautiful design into a beautiful print. Programmes such as InDesign or Acrobat, to name the most widely used, have long had preflight tools, i.e. checking for errors in layouts and PDFs. These checks are indispensable but not enough by themselves: they do formal assessments according to predefined standards but do not know the context. So what is needed is proper design upstream and conscious checking downstream. Here is a reasoned checklist summarising the most common problems that it is essential to be aware of, useful before handing over PDFs to the printer. The always good rule is: when in doubt, reason not as a graphic designer but as a printer, or better yet, talk to them.

Work organisation
Often the elements of a graphic project arrive at different times and are not immediately finalised, so you start to layout without properly organising the work, with the images and fonts scattered around the computer or, worse, in the folders shared with the workgroup. Due to a mistake or an oversight, some files may be modified or deleted, and when the time comes to do the PDF, you find yourself with missing images or fonts. As soon as you have consolidated your project, save it with the Package command, which creates a folder in which InDesign collects the InDesign file with the .indd extension, the one with the .idml extension (which can be opened with previous versions of the programme), the PDF file of the work, the folder containing all the fonts used in the document and the one containing all the images and other external links. When you add elements, you only have to insert them into this structure or modify those already present. When you do the PDF print, all the components will be available, and you only have to redo the package to have the archive of the executive's native files as well.

Page format
If you start to layout a document from scratch, the first thing InDesign asks for is the size of the pages; once this is set, they will all be the same - even if you add more - unless you adjust the size of each one. In itself, having different-sized pages in the same layout is not a mistake; it becomes one if the print was to have all the same pages.
Let's think about the flap cover of a paperback: the correct way to set up the document is to create five pages side by side and set the measurements of the left flap, outside back cover, spine, front cover and right flap. If we do the PDF with the document laid out, we will have the cover and its fold and cut marks—the same if we were to typeset an 8vo hinged. But the pages must be the same for laying out a book or a catalogue. The printer at the imposition stage creates a document with the dimensions of the closed format of the print and centres each page of the supplied PDF. If the pages are different, the smaller ones may show cross marks. Be especially careful if you create editorial prints in which the materials come from other sources (e.g. advertising pages inserted in a magazine) or assemble a document in Acrobat using pages that come from different PDFs: enable the preferences ‘Always show the document page size’ and Show ArtBox, TrimBox and BleedBox, so you always have evidence of the page geometry. Furthermore, you will have the exact page size with the ‘Set Page Bounding Boxes' command under Margin Controls.

MediaBox, TrimBox and BleedBox
They identify the different areas of the page: the MediaBox represents the media size and contains all other boxes; the TrimBox represents the trim area and defines the size of the finished trimmed job beyond which there is the BleedBox, i.e. the bleed area, which should be at least 3 mm. These are the minimum areas that each PDF must have to go to print. In particular, the trim and bleed areas are indispensable for ripping and imposition operations that rely on them. You will have the three defined areas and the necessary abundances by automatically setting the PDF creation settings and having all the graphic elements beyond the trim.
There is also the CropBox (or trim box), which generally coincides with the Media box and corresponds to the area displayed in Acrobat, and the ArtBox, which identifies the area of the page inside the Trim within which to keep the elements that do not go beyond the trim (at least 5 mm) and is also the area used when the PDF is imported into another software.

Single pages
Unless you have covers, flyers or other special layouts for which the printer explicitly requests it, never provide PDFs of laid-out documents: you can easily layout side-by-side, but when producing the PDF, the option Side-by-side pages must be unchecked, and PDFs must be single-page.

Page sequence
Pagination already has its complexities and variables, so why complicate your existence by altering the sequence of pages by trying to put them in machine-fall? That's about as bad as it gets. Even if you have to print a very simple 16mo staple, leave it to the printer. Their job is to decide how to set the fold and, consequently, the marking. Just put the number on the page, if it is provided for in the graphic design, and number the pages correctly with the Numbering and Section Options command, which allows you to set the page and section numbers (e.g. Roman numerals for apparatus and Arabic numerals for text). This way, the PDF will reflect the correct numbering and indicate to the printer the sequence, page numbers and page number within each section.

Bleeds
Even if you are typesetting a running black textbook with no cutting elements, the PDF must never be provided with bleed. It must have Trim and BleedBox and all print marks: cut marks, registration markers and page information. And the BleedBox and the indication area must be defined. In InDesign, these settings are in the Bleed Page Indicators tab. In particular, the bleed page measures depend on how the document was set up at the time of creation. At that stage, it is necessary to set the Bleed Page Measurements (3 or 5 mm per side), i.e., how many millimetres the bleed area will be, at what distance from the Trim the print marks will be placed, and the Indication Area. In this way, you only need to enable Use bleed page settings in the document without worrying about anything else. By setting the page-to-live measurements right away, the document will appear with a useful outer border to know how far to extend images and graphics. Just be careful not to confuse these measures with Margins, which instead define an area inside the page within which to stay to avoid placing graphics too close to the page border (e.g. the page numbers of a staple with many pages).

If you give them a bleed-free document with no bleeds, the printer will centre the PDF in the format: if there are no bleeds, it might not be a problem, but with bleeds, there will be no bleeds and no matter how precise the cut and how good the bookbinder is, it is unthinkable to cut perfectly where the colour ends so you will see an unpleasant white line between the end of the colour and the end of the paper.

Marks
A page with no markers is equivalent to a bleed page area for the printer, who will wonder whether they should stick to the file or the measurements you handed them with the job description. Some self-styled graphic designers have the bad habit of creating a document (MediaBox) in A4 format and centring the page in it in the format to be trimmed, then exporting the PDF without the marks: these are often text-only documents which, due to inexperience, are "paginated" in Word without defining the correct page format and without being able to insert the marks. Now, apart from the inappropriateness of using a word processor to layout and create print PDFs, which is, moreover, indirectly permitted by the fact that the text remains vectorial and therefore printable, it would be sufficient once the PDF has been created, to modify the page size in Acrobat (Preliminary Verification/Actions/Pages/Create bleed page area) and add the crosses from Add clipping indicators and bleed page.

Format and foliation
When designing a print, not only its runnability but also its optimisation should be considered. The square format, for example, is very nice, but it has very high paper waste and constrains the packaging. Similarly, consider the number of pages: theoretically, it is enough if it is a multiple of four, but it depends on the signatures. While it might be fine for a book to have a few blank pages at the bottom to square off, this is not the case for almost all other printed matter. Often having a signature split can affect costs. Therefore, think about 8vi and 16mi, i.e. optimal signatures, and discuss this with the printer.

Document with low-resolution images
While vector images can be enlarged indefinitely without loss of quality and definition, for raster images, resolution (and not definition, as found in many tutorials) is decisive for print quality. The resolution of a paginated image, i.e. one sized for the page, should generally be between 240 and 300 dpi; vice versa, lower resolution or excessive enlargement results in pixelated images. It is good practice to bring all images to high resolution before putting them on the page so that you know their actual size in print resolution. Be careful not to shrink huge images too much because you risk moiré.
You can, however, force the resolution via Photoshop's Resample by activating Retain Detail 2.0, which increases missing pixels, interpolating existing ones with special AI algorithms, as long as you don't overdo it (Reduce Noise possibly reduces artefacts), or you can use the new Super Resolution feature, introduced in Camera Raw 13.2, which creates an image with double the size of the original or four times the total number of pixels.

In any preflight system, insufficient resolution is well highlighted, indicating the document's actual size, position, and resolution on the page. Attention is also paid to the compression factor, i.e. how much an image has been compressed: the greater the compression, the greater the potential loss of quality (above 10x an error is reported). High images reported to have a high compression factor should be checked on time.

Spot colours
Using spot colours is only permissible if it is part of the design. If we only print in four-colour process, all spot colours must be converted before exporting the PDF and consciously, i.e. checking that the result is as expected. Conversion at the time of the PDF or even left to the printer, who will certainly convert in the best way but still arbitrarily compared to expectations, is not the best choice. Spot colours can be used for die-cuts, for the mask of the varnish or for other enhancements such as embossing or debossing, but they must be placed in a dedicated and indicated layer. When checking, use the profile congruent with the number of colours expected in the print job: if the job is a 4-colour job, use a profile that excludes the presence of spot colours; if the job is a spot colour only job or includes at least one spot colour, use a profile that provides for them.

Converting to CMYK
Leaving elements in RGB in print PDFs "because the printer will fix it later" is wrong because, however best the printer can do it, the resulting colour might be numerically correct but not be what you expected. And the alibi 'I convert at the last moment because I don't know how I will print the job' is not valid either because the last moment is not when I deliver the PDF, but when I make the PDF to be delivered. The correct flow, once and for all, is to post-produce in RGB and create a sort of digital parent from which to start for each intended channel: then, in the case of printing, to proceed with the conversion to CMYK at the moment when an image begins its process to be printed, i.e. it is paginated. And this applies all the more to the application of profiles.

Similarly, when typesetting, create or convert colour swatches to CMYK immediately, or spot colour if it is envisaged, and do not leave any colours in different spaces. In fact, before making the final PDF, remove unused colours. In this way, colour proofs from the PDF will also be reliable as long as they are made according to certification standards.

Preview output
The Acrobat function is handy for checking the different colours of a PDF against a simulation profile. From the simulation profile shown in the document, activate Simulate overprinting to prevent overprinting and perforation. By default, each object inserted in the document perforates all the elements below to mask small outliers. In InDesign, overprint preview is deactivated by default, so it must be activated to see evidence of it.

An exception is the K 100: if it overlaps another coloured element, it lets what is underneath show through. This is fine for text, but a backing takes on excessive force at the overlapping points. In this case, deactivate overprinting. In Preview under Separations, check that the maximum coverage of the colour sum does not pass 310% and that the colours present will be used in print. If an unexpected spot colour appears, you must redo the PDF with the correct Print Default. Activate Total Area Coverage and set the value to 320%: all areas with excessive ink coverage will be highlighted in green. Finally, if you have spot colours or channels used for special processes such as reinforcement colours, die-cut traces, varnish reserves or other enhancements, activate or deactivate the individual colours in Separations to check that they work as intended. In this case, when preparing your artwork, give the spot colours of the workings an identifying name so that they are distinct from the print colours.

Minimum colour values
We have mentioned the maximum colour coverage, which should be at most 310% to avoid rejection, drying and counter-printing problems, but minimum values must also be considered. Tiny graphics with low colour percentages risk appearing incomplete, almost "smudged": the emblematic cases are texts in graffiti fonts or fine threads. It is no coincidence that preflight programmes warn if there are extremely fine lines: avoid lines under 2 pt and texts under 5 pt. If you can reproduce thicknesses of 0.1 pt in offset, it may not be possible in digital. Furthermore, paper absorption and plate writing tolerances suggest avoiding extremely light screens. Lastly, when constructing the colour palette of a project, eliminate very low percentages of ink because they can cause instability at the printing stage and make the colour differ not only between different runs but also within the same run.

Hollowed graphics
Attention must also be paid to minimal graphics for hollowed-out or perforated text or elements. If a coloured positive text exposes itself to the risk of out-of-register with unsightly splitting, the effect on negative texts is to have the graces, eyelets and punctuation marks closed, sometimes illegible. Once again, beware of tiny texts.

Embedding fonts
When exporting a layout to PDF, ensure you have set 100% to Embed fonts if the % is lower. This way, even if only one font is in a particular font, all that font will be embedded in the PDF. In this way, making even a small text change directly in the PDF file will be possible. Problems with the reproduction of a font will be avoided, especially if the font uses simulated attributes (the locally imposed bold or italic and not the corresponding Bold or Italic font): in this case, the recommendation to use the character and paragraph style sheets that use the correct subset of the font always applies. Correct font embedding is verified in Acrobat in the Font tab of the Properties or the Preliminary Verification report, with the advantage of seeing where the font is used. If a font is 'partially embedded', only the characters used in the document have been included: for printing, this is enough, but changes may not be possible.

Fonts converted to layout
Only convert a text to layout if a logo or font is used for graphics or large titles that must maintain certain characteristics without modification. All other texts, especially long ones, must not be laid out. At one time, this was done to avoid compatibility problems, but today it is no longer necessary. It is a harmful practice since the text is no longer editable, the file with layouts is much heavier, and another copy must always be kept with the fonts not laid out in case changes are needed (and nine times out of ten, this is the case). Finally, the layout is never faithful to the original and has altered graces, eyelets or curves. For the same reason, do not raster text: becoming images exposes you to all the problems of an image with the aggravating factor that they lose definition compared to a font.

Correct use of black
K100 black is used for text or fine black graphics and not for backgrounds or all-black elements that overlap other coloured ones. Black alone, even at maximum density, on backgrounds appears washed out and drained, almost grey, especially if the paper tends to absorb it. There are two options depending on the risk of off-register. One is to use a black reinforced with 50% of a second colour, which will, however, inevitably have a dominant depending on the colour chosen (usually cyan or magenta) or the "rich black" made from the four-colour process obtained with different combinations. Every graphic designer has their recipe; it is important to avoid exaggerating with ink percentages, which should not pass 310% when added together. Remember that in Photoshop, there is four-colour black (C75, M65, Y60, K80 with 280% opacity), which is obtained by converting flat black from RGB space to CMYK, and the so-called Photoshop black (C91, M79, Y62, K97 with 330% opacity). While in InDesign, the basic black is K100, other blacks are obtained by compositing them with the four inks, like any other colour. Black [Register] is never used: it is a colour sample, which cannot be modified or removed, obtained from the maximum percentage of the four colours, which is reported in each channel and is used for print marks.



Overprinting, perforation, transparencies and shadows
When paginating, some objects can overlap others. Normally, all colours on the upper layer, when output, perforate those below. On the other hand, black is the darkest colour and should overprint, but K100 makes the underlying image show through. To get around this problem, set it to perforation only where needed.

The PDF
Today, making a PDF print is a matter of a couple of clicks, but they must be the right clicks. Let's start with InDesign, the de facto standard for page layout: the command is Export; the old method of "printing" the PDF in PostScript and then distilling is no longer to be used because it is obsolete and, among other things does not support ICC profiles nor transparencies and requires an interpreter, which means that it does not convert your page layout correctly into PDF.

After choosing the export folder, the key options are in General, Adobe PDF Preset, Standard and Compatibility. The [High-Quality Print] preset is insufficient for printing because it does not operate any colour management. [Typographical quality], on the other hand, converts the output colours according to the chosen profile and optimises the compression of high-resolution images but does not certify the PDF and, above all, has limited compatibility with Acrobat 5 (PDF 1.4), which is now obsolete. If you need the printer's profiles or need to know which ones to use, use those of the Ghent Workgroup. You will find the correct profiles for the different technologies on the site: GWG_SheetCmyk_2015 CMYK for four-colour printing and GWG_SheetSpot_2015 CMYK for spot colour printing. The PDF so is PDF/X-4:2010 certified and Acrobat 7 compatible (PDF 1.6), exports all visible and printable layers, will not downsample the resolution of the images while preserving the original, but will compress text and graphics by cropping the images to the box in which they are paginated; indicators and specifications of the bleed areas (not the bleed areas you have to give to the elements in the bleed page area) are set, colours handled correctly and fonts included. Acrobat's Prepress library also indicates these profiles as GWG 2015.