Flatten PDF
Lock form fields and comments into the page so they can’t be changed.
A filled-in form can still be changed by anyone who opens it, and some portals reject PDFs that have live fields. Flattening draws every answer, checkbox and comment into the page itself, so the document looks the same in every viewer and can no longer be edited.
How to flatten a PDF
- Choose one or more PDFs.
- Pick what to flatten: form fields, comments and markup, or both.
- Click “Flatten PDF” and download the locked copy.
Frequently asked questions
What does flattening a PDF mean?
It turns interactive parts of a PDF, such as form fields and comments, into ordinary page content. The answers stay visible and print the same, but they can no longer be typed into, unticked or deleted.
Why would I flatten a filled form?
So nobody can change your answers after you send it, so the answers show up in viewers that don’t display form fields properly, and because some upload portals and e-filing systems only accept flat PDFs.
Can I unflatten a PDF?
No. Flattening is permanent, so keep your editable original in case you need to change an answer later.
Does it keep links working?
Yes. Links are left as they are. Only form fields and comments are flattened, and you can choose just one of the two.
Are my files uploaded to a server?
No. ModifyPDF processes files with JavaScript inside your browser. Your documents never leave your device, and nothing is stored after you close the page.
What gets flattened
Form fields: typed answers, ticked checkboxes and radio buttons, drop-down choices and signature images, each drawn exactly where it appeared. Comments and markup: highlights, sticky-note icons, stamps, shapes, ink drawings and typewriter text. Pop-up note windows and comment replies don’t show on the page, so they are removed with their comment.
What stays the same
Page text, images and links are untouched, and hidden fields stay hidden. If a form was filled in an app that didn’t save how the answers look, fresh appearances are made from the values before flattening, so the answers don’t disappear.
Flatten after filling and signing
A common order is: fill the form with Fill PDF form, add your signature with Sign PDF, then flatten the result before you email or upload it. Fill PDF form also has a “Flatten” option that does this in one step.
Digital signatures
Flattening changes the file, so a certificate-based digital signature added earlier will show as invalid. Flatten first, then apply a digital signature, if you need one.