How to make a print-ready PDF

To a printer, print-ready is not a feeling. It is a short list they check every file against, and a file that fails one item comes back to you, or gets printed with a white sliver along one edge. Here is the list:

PDF/X is an ISO standard for exactly this job: a PDF whose fonts are embedded, whose page says where it will be trimmed, and which names the printing condition its colours were made for. It is a floor, not a guarantee. Bleed and resolution are not part of it.

Then check what came out. The rest of this guide is how, and it works the same on a PDF from any app, including one somebody sent you.

Check a PDF you already have

Five commands from Poppler and Ghostscript cover everything on the list except the safe margin, which you check by eye. Install them with brew install poppler ghostscript qpdf imagemagick on a Mac, or apt install poppler-utils ghostscript qpdf imagemagick on Debian and Ubuntu. On Windows, run them in WSL.

The examples use two files of the same A5 flyer. flyer.pdf was saved from an app with no print settings. print.pdf is a PDF/X-4 export with 3 mm bleed.

Size and bleed

pdfinfo -box print.pdf | grep -E "Page size|Box"

Page size:       436.54 x 612.28 pts
MediaBox:            0.00     0.00   436.54   612.28
CropBox:             0.00     0.00   436.54   612.28
BleedBox:            0.00     0.00   436.53   612.28
TrimBox:             8.50     8.50   428.03   603.78
ArtBox:              0.00     0.00   436.54   612.28

The numbers are points: divide by 2.835 for millimetres. The TrimBox is where the guillotine cuts: 428.03 − 8.50 = 419.53 pt wide, which is 148 mm, the width of A5. The page itself is 8.50 pt (3 mm) bigger on every side, and that margin is the bleed.

flyer.pdf gives a different picture:

Page size:       419.53 x 595.28 pts
MediaBox:            0.00     0.00   419.53   595.28
CropBox:             0.00     0.00   419.53   595.28
BleedBox:            0.00     0.00   419.53   595.28
TrimBox:             0.00     0.00   419.53   595.28
ArtBox:              0.00     0.00   419.53   595.28

Every box is the page. That file has no TrimBox at all: when one is missing, pdfinfo prints the page size in its place. Either way the answer is the same. The page is exactly A5, so there is no bleed, and a background that touches the edge will show a white line wherever the cut drifts. How to add bleed and crop marks covers the fixes.

A box in the right place does not prove the art fills it. Look at the edges of the page: the background has to run all the way out.

Fonts

pdffonts flyer.pdf

name                                 type              encoding         emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
Helvetica-Bold                       Type 1            Standard         no  no  yes      8  0
Helvetica                            Type 1            Standard         no  no  yes      9  0

no under emb means the font is not in the file, so the printer's machine uses whatever it has under that name. Every row has to say yes. In print.pdf they do, and the six letters before the name (UVSAXG+Helvetica-Bold) mean only the characters used were embedded, which is normal. A PDF with text turned into outlines lists no fonts at all.

Images

pdfimages -list flyer.pdf

page   num  type   width height color comp bpc  enc interp  object ID x-ppi y-ppi size ratio
--------------------------------------------------------------------------------------------
   1     0 image     600   400  rgb     3   8  jpeg   no         7  0   119   119  139K  20%

Two columns matter. x-ppi is the resolution at the size the image is placed: 119 here, where print wants about 300. color says rgb. In print.pdf the same photo is 1800 pixels wide and comes out at 357 PPI and cmyk. If a photo is too small, no export setting fixes it; see how to check an image is sharp enough to print.

An rgb image is not automatically wrong. PDF/X-4 allows colour-managed RGB and converts it at the printer. PDF/X-1a does not allow it at all. If the printer asks for CMYK, convert RGB to CMYK for print before you send.

PDF/X, and which printing condition

pdfinfo print.pdf | grep "PDF subtype"
qpdf --json print.pdf | grep -o '"/OutputConditionIdentifier": "[^"]*"'

PDF subtype:    PDF/X-4
"/OutputConditionIdentifier": "u:FOGRA39"

The first line is the claim. The second is the output intent, the printing condition the colours were prepared for (FOGRA39 is coated paper on a European offset press). A real PDF/X file has both; check the condition is the one the printer asked for. flyer.pdf prints nothing for either, so it isn't PDF/X. The qpdf line needs qpdf 11 or later.

Ink

gs -q -o - -sDEVICE=inkcov print.pdf

 0.87878  0.98460  0.45626  0.36091 CMYK OK

One line per page: how much of the page each ink covers, cyan, magenta, yellow and black, from 0 to 1. It is useful for one question: does a page that should be black only, a text page in a book, use only black? Don't read more into it. It is an average over the page, and it converts RGB as it goes, so the RGB flyer.pdf also reports CMYK OK.

What a printer worries about is the total ink at the darkest point: cyan, magenta, yellow and black added together. Too much and the sheet doesn't dry. Render the page in CMYK and take the maximum:

gs -q -sDEVICE=tiff32nc -r150 -o page-%02d.tif print.pdf
magick page-01.tif -separate -evaluate-sequence mean -format "%[fx:round(maxima*400)]%%\n" info:

240%

That is the rich black band at the bottom of the flyer, 60/40/40/100. The printer's spec sheet gives the limit, commonly around 300 % on coated paper. flyer.pdf's plain RGB black, converted for FOGRA39, came out at 299 %, right on that line. Run the second command once per page file.

This quick version is exact for CMYK, but it measures RGB through Ghostscript's own default profile rather than the printer's. For RGB content, a map of where the heavy areas are, and which ink causes them, see how to check total ink coverage.

Making PDF/X with Ghostscript

If your file is otherwise right (size, bleed, resolution) and only the PDF/X part is missing, Ghostscript can write it. It needs two things: the ICC profile for the printer's condition, and a short file that declares it. On Debian and Ubuntu the FOGRA39 profile is in the colord-data package; on a Mac or Windows, download ISO Coated v2 from the ECI (eci.org), which is the same condition. Use the profile the printer names.

Save this as pdfx4.ps, next to the profile:

%!
[ /GTS_PDFXVersion (PDF/X-4) /Title (Summer Fair flyer) /Trapped /False /DOCINFO pdfmark
[ /_objdef {icc} /type /stream /OBJ pdfmark
[ {icc} << /N 4 >> /PUT pdfmark
[ {icc} (FOGRA39L_coated.icc) (r) file /PUT pdfmark
[ /_objdef {intent} /type /dict /OBJ pdfmark
[ {intent} << /Type /OutputIntent /S /GTS_PDFX
    /OutputConditionIdentifier (FOGRA39)
    /OutputCondition (Offset printing, coated paper)
    /RegistryName (http://www.color.org)
    /DestOutputProfile {icc} >> /PUT pdfmark
[ {Catalog} << /OutputIntents [ {intent} ] >> /PUT pdfmark

Then:

cp /usr/share/color/icc/colord/FOGRA39L_coated.icc .
gs -dPDFX=4 -dPDFSETTINGS=/prepress -sDEVICE=pdfwrite \
   -sColorConversionStrategy=CMYK -sOutputICCProfile=FOGRA39L_coated.icc \
   --permit-file-read=FOGRA39L_coated.icc -o print.pdf pdfx4.ps artwork.pdf

On Windows the command is gswin64c. That is how print.pdf above was made, by Ghostscript 10.05.1: the photo converted to CMYK with the FOGRA39 profile, the CMYK colours already in the file left exactly as they were, the fonts embedded, the TrimBox and bleed kept, and the output intent written.

What it doesn't do matters as much:

• It doesn't check anything. The same command on flyer.pdf produced a file labelled PDF/X-4 with no bleed and the photo still at 119 PPI. It added a TrimBox the size of the page, because PDF/X requires one.
• It embeds lookalikes for missing fonts. flyer.pdf's Helvetica wasn't in the file, so Ghostscript embedded its own Nimbus Sans under that name. Close, but not the font you designed with.
• Without the definition file it still says PDF/X. -dPDFX=4 alone wrote PDF/X-4 into the file's metadata with no output intent at all, which is not a valid PDF/X file. The qpdf check above catches that.
• Read the error, not the file. Ghostscript prefers its own PDFX_def.ps (an example with a placeholder profile) over one of the same name in your folder, which is why the file above has a different name. A run that stopped on an error once left a blank A4 page labelled PDF/X-4 behind it.

It is an honest tool for a narrow job. It isn't a preflight.

No design software

If all you have is Word, a phone or a Chromebook, you can't set a bleed or export PDF/X. Your options are a design app (Scribus is free on Windows, macOS and Linux), asking the printer what they accept, or a design editor in the browser.

Two things to know before you start. Its output profiles are the US ones (GRACoL 2013, SWOP 2013, GRACoL 2006), so if your printer asks for FOGRA39 or another European condition, ask whether GRACoL is acceptable. And it turns text into outlines in the print PDF, so check spelling before you export. Then run the checks above on what it gives you, like any other file.

Spot colours, folds and finishes

A job with a Pantone colour, foil, white ink or a die line needs those as named spot colours, each on its own plate, named exactly as the printer asks. That is its own subject: how to match a Pantone colour in CMYK. Folded leaflets and books have their own page arrangements; the printer will send a template.

Before you send it

Most printers check the file again when it arrives and tell you if something is wrong before they print. A file that passes these checks means that email doesn't come.