Drop a document above. It is read first — how many pages, how many form fields, how many comments — and then you choose what "flatten" meant.
Nothing is uploaded. The document is opened, changed and saved inside your browser.
"Flatten" means three different things
This is the whole reason this page reads your file before it offers you a button. Every other flatten tool picks one of these three silently and hopes it was yours.
1. Merge the form fields into the page. Somebody filled in a form, and you want it to stop being a form: no more typing, no more accidental changes, and the values are part of the page now. The text stays text — searchable, selectable, and sharp at any size. This is what Acrobat's Flatten does and what most people mean.
2. Turn every page into a picture. Nothing can be edited, selected or copied afterwards — including the text, which stops being text. The file gets larger and its resolution is fixed from then on. Useful when the point is that nothing can be lifted out of the document.
3. Flatten transparency. What a print shop means, every time. It is a prepress operation — resolving live transparency so an older RIP can output the job — and this page does not do it, because it needs a RIP. See below.
What this page does not do: transparency
If a printer asked you to "flatten the file", this is almost certainly what they meant, and no browser tool can do it. Transparency flattening happens in a RIP, in Acrobat's print production tools, or in the layout application you exported from — and it changes how the artwork is rendered for output, not what the document contains.
Nothing on this page changes how transparency in your file will be output. Saying so plainly is more use than a green tick, and it is the difference between a tool and a trap.
What usually solves it: export again as PDF/X-1a, which flattens transparency as part of the standard, or ask the printer which PDF preset they want. If the problem is a specific effect — a drop shadow, a blend mode — the layout file is where it gets fixed.
Which one should you pick?
The page tells you what your document contains, which usually settles it:
- It has form fields → merge them. Nothing is lost and the text survives.
- It has comments or stamps on it → merging the fields leaves those alone. Only the picture route removes them.
- It has neither → there is nothing to merge, and the picture route is the only flatten left.
Resolution, and the number this page prints
If you take the picture route, you choose the resolution: 96 dpi for something that only has to be readable on a screen, 150 for large format seen from a step back, 300 for something held at reading distance.
The page tells you the resolution you will actually get, which is not always the one you asked for: every page is capped at 4,000 pixels on its long edge, so 300 dpi on an A4 page is 300, and on an A3 page it is about 242. Tools that report the number you typed are quietly wrong, and the people who find out are the ones sending the file to a press.
What flattening does not fix
- It does not make a low-resolution image sharp. Check that with the PDF DPI checker instead.
- It does not change colour, convert to CMYK, or embed fonts.
- It does not remove hidden content that was never visible — a flattened page shows what the page showed.
- The picture route makes the file larger, often much larger, and stops it being searchable.
When the file is not really the question
Flattening is usually the last step before sending something to somebody. What happens after that is where the cost is: a proof emailed round, three comments in a reply, a revision, and somebody approving a version nobody meant. That is what Proofavo is for — a proof link your customer opens without an account, comments pinned to the artwork itself, and a record of who approved what and when.
The other free tools here: crop a PDF in real millimetres, compare two PDFs visually, and annotate a PDF with arrows and numbered notes.