Flattening turns the interactive parts of a PDF into ordinary page content. The answers typed into a form, the ticks in its checkboxes, and the highlights, stamps and sticky notes added during a review are all drawn onto the page exactly where they sat, and the editable objects behind them are removed.
The result looks the same as the file you started with, but nobody can change the answers or move a comment afterwards, and no PDF reader will offer it as a fillable form. That is what you want when you send a completed tax form, a rental application or a school enrolment form to someone who should read your answers rather than edit them.
Drop in one PDF of up to 100 MB. You get back a copy ending in -flattened.pdf, with a short note telling you what was done, for example “Flattened 12 form fields and 3 comments or stamps.” Your original file is left as it was.
How to flatten PDF
- Add your PDF. Drop it on the box above or tap to choose it. One file at a time, up to 100 MB.
- Choose what to flatten. Both options are ticked by default: Flatten form fields, and Flatten comments, highlights and stamps. Untick either one to leave that part editable.
- Flatten and download. The new file ends in -flattened.pdf, and the note under the button tells you how many fields and comments were flattened.
What happens to form fields and comments
Form fields. Text boxes, checkboxes, radio buttons, dropdowns and signature fields each have a current value. Flattening draws that value into the page as normal content and deletes the field. A ticked box becomes a printed tick, a dropdown becomes the words that were selected, and the form stops being a form. If a value is written in a script the standard PDF fonts cannot draw, such as Chinese or Arabic, the appearance already saved in the file is used rather than being redrawn, so the characters come out as they were displayed.
Comments and markup. Highlights, underlines, sticky-note icons, stamps, shapes, freehand ink and typed text boxes each carry a stored appearance. That appearance is painted onto the page in the same position and the annotation is removed. Hidden annotations are deleted. The pop-up windows attached to sticky notes go too, so the note icon stays visible on the page but clicking it no longer opens the text inside.
Links are left alone and stay clickable. An annotation with no stored appearance, which turns up occasionally in files from older software, is also left as it was rather than guessed at. If there is nothing to flatten at all, the tool says so: “This PDF has no form fields or comments to flatten. It is already flat.”
When flattening solves a real problem
Printing filled-in forms. Some printers and print drivers print the blank form and drop the values typed into its fields. Once the answers are part of the page, they print like any other text. If a completed form keeps coming out of the printer empty, flatten it and print the flattened copy.
Merging two copies of the same form. Field names inside a PDF must be unique. Combine two copies of the same form, say two staff members’ timesheets, and the duplicate names collide, so typing in one copy can overwrite the other or wipe the values entirely. Flatten each copy first, then join them with Merge PDF, and both sets of answers survive.
Upload portals and final versions. Some government and university upload portals reject fillable forms or ask for a non-editable copy. Flattening is also a clean way to finish a review: the highlights and stamps from the last round become part of the document, so the version you file or send matches the one that was signed off.
Limits worth knowing
It cannot be undone. A flattened field is just text and lines on the page. There is no switch that turns it back into a field, so keep the original if there is any chance you will need to change an answer or reuse the blank form.
It is not redaction. Flattening a black highlight over a name paints the highlight onto the page, but the name underneath is still in the file and can usually be selected, copied or found by search. If text has to be removed for privacy, flattening is the wrong tool.
Partial flattening is fine. Untick Flatten comments, highlights and stamps to lock the form answers but keep the review comments editable, or do the reverse to bake in a reviewer’s markup while leaving the form fillable. Each option works on its own.
Questions people actually ask
How do I make a PDF form non-editable?
Flatten it. Add the filled-in form, leave Flatten form fields ticked and download the result. Every field’s current value is drawn onto the page and the field itself is removed, so the answers look the same but cannot be changed and no reader will show the form as fillable.
Can a flattened PDF be unflattened?
No. Once a field or comment is flattened it is ordinary page content, the same as the printed text around it, and there is nothing left to turn back into a field. Keep a copy of the original file if you might need to edit the answers or fill in the form again.
Why do my filled-in form answers disappear when I print?
Some printers and print drivers print the page underneath a form but skip the values stored in its fields, so you get a blank form. Flattening draws the answers onto the page itself, and from then on they print like any other text. Print the flattened copy instead of the original.
Does flattening a PDF hide highlighted or covered text?
No. Flattening paints the highlight, box or stamp onto the page, but the text beneath it is still stored in the file and can usually be selected, copied or found with search. Flattening is not redaction, so do not rely on it to remove private information before sending a document.
How do I flatten annotations in a PDF but keep the form fillable?
Untick Flatten form fields and leave Flatten comments, highlights and stamps ticked. The highlights, notes, stamps and drawings are painted onto the page and removed as annotations, while the form fields stay editable. Links are kept clickable either way, and the note tells you how many comments were flattened.