How to Flatten a PDF (Free, No Acrobat)

Flattening turns things that can still be changed into part of the page itself. A filled-in text box stops being a field and becomes printed text. A highlight, a comment stamp or a signature image stops being an annotation sitting on top of the page and becomes part of what is drawn. After that, nobody opening the file can edit the field values or drag the annotations away. Flatten when you are sending a completed form to someone who should not change it, when a viewer shows your filled values as blank, or before merging files whose form fields would otherwise collide. It is a one-way trip, so keep your original. Flattening is not security: it does not add a password and does not remove hidden text or metadata. For that, see redaction.

Use form mode if the only thing you need locked is fillable fields. It is lossless: each field's current appearance is drawn onto the page and the form layer is removed, so the text on the page stays selectable and the file size barely changes. Use whole-document mode if you also have comments, highlights or signature stamps. Form mode does not touch those, because no standard library call flattens generic annotations. Whole-document mode redraws every page as an image, which bakes in everything you can see. The cost is real: text is no longer selectable or searchable, and the file usually gets bigger. If you are unsure, try form mode first and open the result. If a comment is still movable, rerun in whole-document mode.

Open the Flatten PDF tool and drop your file in. Nothing is uploaded: the work happens on your device. Choose form fields or whole document, then run it. Download the result and open it in your normal viewer to check three things: the filled values still show, the fields can no longer be clicked into, and any comment or stamp you wanted baked in cannot be selected. Save it under a new name so the editable original survives. If you still need to fill the form first, use the Fill PDF Form tool, then flatten the finished copy. A signed document should be flattened after the signature is placed, never before.

The tool tells you when there is nothing to do instead of handing back an identical file. Form mode reports it when the PDF has zero fillable fields. Whole-document mode reports it when there are no fields and no annotation that actually draws something on the page. A plain link is the usual surprise: it is a clickable region with nothing visible to bake in, so a PDF whose only annotations are links counts as already flat. This also explains a common complaint, "I flattened it and nothing changed". If the document was printed to PDF or exported from a design tool, its content was probably flat to begin with. Scanned PDFs are the same, since the page is already one image.

Form mode leaves size almost unchanged. Whole-document mode is different because every page becomes a JPEG image rendered at twice its normal resolution, at 85 percent quality. That keeps small print legible, but a text-heavy 200 KB document can grow several times over, because vector text is replaced by pixels. Two practical consequences follow. First, you cannot copy text from the result, so keep a searchable original or run OCR afterwards if you need search. Second, if the file is now too large to email, run it through the compress tool, accepting a further small quality drop. Avoid whole-document mode on long documents that are mostly plain text unless you truly need the annotations baked in.

Check which viewer you are using and which mode you ran. A highlight or comment that is still movable means form mode was used, so rerun in whole-document mode. A field that looks filled but shows blank in a phone preview often had its appearance generated only by the original app; flattening in form mode draws the current appearance, so reopen the flattened copy to confirm values show. If the PDF was password-protected, unlock it first. If you plan to merge files afterwards, flatten each one before merging, since duplicate field names across documents are the reason values disappear or get overwritten in a merged form.