Print preflight guides
Each guide answers one question people run into before they send a file to print. Where a number comes from a printer or platform, the guide names the source and the date it was read; where it is common practice rather than a rule, it says so.
The examples are produced by the checks on this site, run on small test files, so you can see exactly what a check reports. Nothing here replaces your printer's own specification. How the checks work, and what they do not cover.
What does a KDP paperback interior PDF need?
Trim size, bleed on three edges, margins by page count, 300 DPI images and embedded fonts. KDP's published numbers, and what a check can and cannot verify.
What are Adobe Stock's technical requirements for photos?
JPEG, sRGB, 4 to 100 megapixels, 45 MB at most. Adobe's published photo requirements in one table, which of them a file check can verify, and what happens at the edges.
Why does Adobe Stock refuse photos for quality?
Adobe asks for a sharp main subject, minimal noise and artifacts, and balanced light. What each means, and what software could and could not catch on 96 real photos.
What counts as similar content on Adobe Stock?
Adobe lists flips, crops, filters and slightly different angles as too similar. Which of those a perceptual hash catches, tested on generated scenes and 14 real photos.
How can you tell if a PDF is ready to print?
There is no single standard for print-ready. Six things printers commonly check, what Adobe and KDP say about them, and a before-and-after run on a test flyer.
Should you use RGB or CMYK for printing?
It depends on your printer: some convert RGB files themselves, others ask for CMYK. What each mode is, what Adobe, KDP and Canva say, and how one PDF gets three different results.
Which PDF box sets the page size: MediaBox, CropBox or TrimBox?
Your viewer says A4 and your printer disagrees. What the five PDF page boxes mean, which one is the finished size, and six test files showing how a checker reads them.
How much bleed do you need for printing?
Most print jobs ask for 3 mm (0.125 in) of bleed, but the right number is your printer's. What bleed is, how big to make the page, and what a bleed check reports.
Why does my PDF say fonts are not embedded, and how do I fix it?
A font that is not embedded is only named in the PDF, so a printer swaps in its own. What embedded, subset and unable to inspect mean, why it happens, and how to fix it.
What DPI do you need for printing?
About 300 pixels per inch at the printed size is the usual target, and the DPI tag stored in the file does not decide it. How to work out your own number, with worked examples.