Flatten a PDF
Merge form answers, highlights, stamps and comments into the page so nothing vanishes when the PDF is printed, emailed or reopened.
- Runs in your browser
- Files are never uploaded
- Free, no account
Flattening turns everything that sits on top of a page — form answers, highlights, stamps, signatures, sticky notes — into part of the page itself, so it prints, emails and renders identically everywhere.
The problem flattening solves
You fill in a PDF form, email it, and the recipient replies that the boxes are empty. Or you print it and the answers are missing from the paper. Or you upload it to a portal and it comes back stripped. Every one of those is the same bug, and it is not your fault.
A PDF page has content — text, lines, images — and it has annotations, which are separate objects that sit above the page: form field widgets, highlights, sticky notes, stamps, ink. Readers are inconsistent about drawing them, printers are inconsistent about printing them, and any process that re-renders the page can drop them entirely. Flattening moves all of it into the page content, after which there is nothing left to be inconsistent about.
What this tool does that most "flatteners" do not
Flattening form fields is the easy half, and every tool does it. The hard half is annotations — a highlight, a comment, a stamp, an ink signature added in Preview or Acrobat. Most tools simply delete them, and because they were often invisible in the first place in whatever reader you are using, you never notice until the printed copy comes out blank.
Every annotation carries an appearance stream: a small form XObject holding the drawing instructions the reader uses to display it. This tool takes that stream, works out the transform that maps the appearance's bounding box onto the annotation's rectangle — the algorithm in ISO 32000-1 §12.5.5 — and draws it into the page's own content. Only then is the annotation removed. That is why comments survive here.
Anything with no stored appearance is left alone rather than discarded, and the result panel tells you how many. Silently deleting something visible is worse than not flattening it.
When to flatten
| Situation | Flatten? | Why |
|---|---|---|
| Returning a completed application form | Yes | Guarantees the reader sees what you typed |
| Sending a marked-up draft to a printer | Yes | Comments print instead of vanishing |
| Archiving a signed contract | Yes | No dependency on future readers' annotation support |
| Circulating a form for others to complete | No | Flattening removes the fields they need |
| Collaborative review still in progress | No | Comments become undeletable page ink |
| Hiding confidential text | No | Flattening is not redaction — see Redact PDF |
Flattening is not rasterising
A common misunderstanding, encouraged by tools that take the lazy route: some "flatten" a PDF by rendering every page to an image. That does make the file uniform, but it also destroys the text layer, kills searchability and screen-reader access, and usually multiplies the file size.
Nothing is rasterised here. Text stays text, vectors stay vectors, images keep their original compression. Only the annotation and field layer changes. If you actively want pages turned into images — for redaction, or to defeat text extraction — that is Redact PDF or PDF to Grayscale, both of which say so up front.
Keep the original
Flattening cannot be undone: once a field's value is page ink, there is no field to restore and no value to read back. The file you drop in is never modified — the flattened copy is a new download — so the safe habit is simply not to delete the original until the flattened version has been accepted.
Questions
Why do my form answers disappear when I print?
Because form fields are annotations that sit above the page, not part of it, and printers and readers disagree about whether to render them. The same mismatch is why answers can vanish when a file is uploaded to a portal, opened on a phone or converted to an image. Flattening moves the answers into the page content, after which there is nothing left to disagree about.
What happens to highlights and sticky notes?
Each annotation carries a stored appearance stream — the drawing instructions a reader uses to display it. This tool draws that stream into the page using the transform the PDF specification defines, then removes the annotation. That is why comments survive here when other "flatteners" silently delete them.
Can flattening be undone?
No. Once a field or comment is part of the page content there is no field or comment left to restore. Keep the original — the tool never modifies the file you dropped in, so the unflattened copy is still on your disk.
Does flattening make the PDF smaller?
Usually slightly, because the form dictionary, the field tree and each annotation's object graph are removed. The text and images are untouched, so do not expect the kind of reduction a compressor gives you — flattening is about reliability, not size.
Should I keep the links clickable?
Almost always yes. Link annotations draw nothing at all, so keeping them costs nothing visually while preserving a working table of contents and any external URLs. Turn them off only if you are deliberately stripping every interactive element out of a document.