You check if a PDF is print ready by inspecting its fonts, image resolution, colour space, bleed and transparency before you send it to a printer. PDF Preflight does all of that in your browser: you drag the file onto the drop zone, the checks run on your own machine, and nothing is uploaded. The results tell you exactly which pages and which objects would cause a commercial press to reject or reprint the job.
What 'print ready' actually means
A PDF that looks fine on screen can still fail at a print shop. Commercial printing imposes requirements that a screen never shows you:
- Fonts must be embedded. If a font is missing from the file, the printer's RIP substitutes something else and your line breaks, spacing and logos shift.
- Images need enough resolution. 300 ppi at final printed size is the usual target for photos and raster artwork. A 72 ppi web image stretched across a page looks blocky on paper.
- Colours must be in the right space. CMYK for process printing, spot colours declared properly, and no accidental RGB blacks that print as muddy four-colour mixes.
- Bleed must extend past the trim. Usually 3 mm (0.125 in). Without it, any background that reaches the page edge gets a thin white sliver when the guillotine cuts.
- Transparency should be flattened or handled deliberately. Live transparency can render differently depending on the RIP.
A preflight check verifies all of this before the file leaves your hands. That is the whole point: fixing a problem in a PDF costs you five minutes; fixing it after a print run costs you the run.
How to check if a PDF is print ready, step by step
- Open PDF Preflight. The page loads with a drop zone labelled 'Drag & drop or browse' and the line 'Processed locally — your files never leave your device'. There is no upload step; the file is read straight from your disk.
- Add your PDF. Drag it onto the drop zone, or browse to it. PDF Preflight takes one file at a time, so if you have a multi-part job, check each part separately.
- Let the checks run. The tool inspects the document structure: embedded fonts, image resolution and effective ppi at placed size, colour spaces, bleed and trim geometry, and transparency.
- Read the report. You get a list of findings tied to pages and objects — for example, a font that is not embedded, an image placed at 140 ppi effective resolution, or an RGB object in a CMYK document.
- Fix what matters. Some fixes you can make directly in PDF Editor — set the document title, add or reposition pages, drop in a corrected image. Others need to go back to the layout application that produced the file.
- Re-run the preflight. After any change, run the check again. A fix in one place can introduce a problem in another, and the second pass takes seconds.
- Send it to the printer. Once the report is clean, the file is ready for the press. Keep the final checked version as your archive copy.
The checks that catch the most reprints
PDF fonts embedded check
Every font used in the document must be embedded, subset or fully. Preflight flags any font that is referenced but not carried in the file. Watch for this especially in PDFs exported from office software, which often embed only the subset of glyphs used and fail when a printer's system tries to edit or impose the file.
PDF image resolution checker
Resolution alone is not the number that matters. What matters is effective resolution: the pixel dimensions of the image divided by the size it occupies on the page. A 3000-pixel-wide photo placed 4 inches wide gives 750 ppi — more than enough. The same photo stretched to 20 inches gives 150 ppi, which is not. A good preflight reports effective ppi per placed image, not the raw file's DPI tag.
PDF bleed check
Bleed is the extra artwork outside the trim line. Preflight compares the page box, trim box and bleed box. If the bleed box equals the trim box, there is no bleed and any edge-to-edge colour will show white slivers after cutting. Most printers want 3 mm of bleed on every edge, and crop marks placed outside it.
Colour and transparency
Preflight reports whether objects are RGB, CMYK, greyscale or spot, and whether the document contains live transparency. Rich black built from RGB values is a common and expensive mistake — it prints as a heavy four-colour mix and can look different on every press.
| Check | What good looks like | What preflight flags |
|---|---|---|
| Fonts | All embedded | Referenced but missing fonts |
| Images | 300 ppi effective at placed size | Below ~200 ppi effective |
| Bleed | 3 mm beyond trim on all edges | Bleed box equal to trim box |
| Colour | CMYK or declared spot | Stray RGB objects |
| Transparency | Flattened or intentional | Live transparency in placed art |
Why checking in the browser beats upload-based preflight tools
Most online preflight services ask you to upload the file to their server. That means your unreleased artwork, client documents, contracts or book layouts sit on someone else's disk, subject to their retention policy and their security.
PDF Preflight runs the analysis in the page, on your device. Your file is never transmitted. That has three practical consequences:
- Privacy. Nothing leaves your machine, so there is no copy to delete, no retention window and no third party in the chain.
- Speed. There is no upload of a 200 MB press-ready PDF over a home connection, and no download of a report. The check starts immediately.
- No file-size caps. Large print files are normal, not exceptional. Because the work is local, file size is limited by your machine, not by a server quota.
The tools are free to use with no account, metered at 5 runs per day; a free account raises that to 15 a day, and a Pro plan unlocks unlimited daily use. A run is one export, however many files it contains. If you regularly preflight production jobs, see /pricing for the unlimited option.
Common mistakes and pro tips
- Trusting the on-screen preview. Acrobat's display does not tell you about missing fonts or low-resolution images. Only a structural check does.
- Checking resolution in Photoshop instead of in the layout. The image may be high resolution in isolation and still be placed too large. Effective ppi is the number that matters.
- Forgetting the second pass. Every fix is a chance to introduce a new fault. Preflight, fix, preflight again.
- Ignoring the printer's own spec. Many print shops publish their own requirements — minimum resolution, required bleed, preferred PDF version. Check their spec first, then use preflight to confirm you meet it.
- Sending the wrong version. Keep your source layout file. If preflight finds a font problem, the fix belongs in the original application, not in a patched PDF.
- Compressing before preflighting. If a file is too large to send, compress it after it passes preflight, not before — compression can drop image resolution below the threshold you just verified. PDF Compressor handles that locally.
- Preflighting only the cover. Interior pages carry the same risks. Check the whole document, not the page that happens to be open.
Related tools that fit the same workflow
Preflight is rarely a one-step job. If the report shows pages in the wrong order, or a page that should not be there, PDF Merger & Splitter reorders, splits and merges pages without uploading the file. If you need to correct a caption, replace a logo, add a page or set the document title after preflight, PDF Editor does that in the browser too. And once the file passes every check, PDF Compressor brings it down to an email-friendly size without sending it anywhere.
What to do when preflight finds a problem
The report is a to-do list, and it is worth reading it in order of severity. Missing fonts and insufficient bleed are usually blockers — they will visibly ruin a print run. Low-resolution images and stray RGB objects are often judgement calls: a 240 ppi image may be perfectly acceptable for a poster viewed from a metre away, and unacceptable for a brochure held in the hand. Colour issues depend on the press and the stock.
Where the fix is structural and belongs in your layout application, go back there and re-export. Where the fix is a page-level edit — a title, a reordered page, a corrected image — do it in PDF Editor and run preflight again. The point of the whole exercise is that by the time the file reaches the printer, there is nothing left for anyone to discover. A clean preflight report is not a guarantee that the job will look good; it is a guarantee that the file will not fail for the mechanical reasons that cause most reprints. That is the part you can control before you press send.