How do I flatten a PDF's form fields or pages?
To flatten a PDF, drop it into FixDoks's Flatten PDF tool and choose Form fields only, which locks filled-in answers while keeping text selectable, or Everything, which rasterises each page to an image at a DPI from 100 to 300. Click Flatten PDF to download. All of the processing happens inside your browser.
Flatten PDF at a glance
| Input | One PDF file |
|---|---|
| Output | Flattened PDF |
| Processing | In your browser; your files are not uploaded |
| Price | Free, no watermark |
| Download | Free Google sign-in |
| Works on | Chrome, Edge, Safari and Firefox on Windows, Mac, Android and iPhone |
How to use Flatten PDF
- Drop your PDF, then choose a mode: Form fields only or Everything.
- For Everything, pick a DPI for how each page is rasterised.
- Click Flatten PDF and download the result.
Two kinds of flattening
"Flatten" means different things depending on what you are trying to lock down, so FixDoks offers two clear modes rather than one setting that tries to do everything.
Form fields only
This mode takes any values already filled into the PDF's form fields and merges them permanently into the page. The page's own text stays vector and selectable, so the file still looks sharp at any zoom level and still allows text search, but the fields themselves are no longer live: nobody can open the file and change what was typed, ticked or selected. This is the natural last step after using Fill PDF form or Fill and sign PDF, before you send a form onward and want the answers to stay fixed.
Everything
This mode is more thorough: it rasterises each page into a single image at the DPI you choose (100, 150, 200 or 300) and rebuilds the PDF from those images. That flattens not just form fields but comments, sticky notes, highlight annotations and any layered content into one flat picture per page. The trade-off is that page text is no longer selectable or searchable afterwards, since the page is now an image rather than text, and file size usually changes: a text-heavy PDF often grows because images take more space than text, while a PDF full of large embedded photos can shrink at a lower DPI.
Choosing a DPI
| DPI | Best for |
|---|---|
| 100 | Smallest file size, fine for on-screen viewing only. |
| 150 | A reasonable balance for emailing or general sharing. |
| 200 | Good detail for most printed documents. |
| 300 | Sharpest output, best for documents with small print or fine diagrams that will be printed. |
Why flatten at all
Flattening is useful when a PDF needs to behave predictably everywhere: some older printers, scanners and office systems render live form fields, comments or layered content inconsistently or not at all, but a flattened page always looks the same. It is also a simple way to make sure a filled form cannot be edited again, or to bake annotations permanently into a document before archiving it.
What flattening does not do
Flattening with "Everything" removes selectable text, which is the opposite of what you want if your goal is a smaller file that stays searchable. If file size alone is the problem, use Compress PDF instead, which keeps text selectable. If you actually want the page to look black and white specifically, use Grayscale PDF, which is a related but separate rasterising step aimed at colour removal rather than flattening layers.
Tips
Keep your original, unflattened file until you are sure you will not need to edit the form or annotations again, since "Everything" mode cannot be reversed. If you only filled a form and want the answers locked, "Form fields only" gives you the smallest quality trade-off since it leaves everything else on the page as sharp vector content.