Flatten a PDF so the form answers cannot be changed

How it works

1. Fill the form in and save it first. Flattening freezes whatever is in the fields at the moment it runs, and an empty field flattens to empty space. Readers can display typed values that were never written to the file, so save before you upload.
2. Choose what gets pressed into the page. Form fields are on by default and comments are off, because the usual case is freezing the answers while leaving the review notes live. Tick both when the annotations are part of the record.
3. Check the result, and file the original somewhere. Open the download: the values should look identical and no longer respond to a click. The notes count what became page content. There is no unflatten, so keep the editable copy.

What the options do

The form above lists the options this tool is running today, straight from the server. This is what they are for.

Flatten form fields

Every filled-in answer becomes ordinary text on the page and the field itself is deleted. Afterwards the form cannot be filled in, cleared or re-typed, and a reader will not offer to. This is what you want before a completed form is filed, signed off, or sent to somebody who might change a figure by accident.

Flatten comments and stamps

Notes, highlights, drawings and stamps become part of the page and can no longer be opened, replied to or deleted. Hidden marks and the popup windows that were never visible on the page are dropped rather than drawn onto it. Links are deliberately left working: a link has no marks of its own, and flattening one would silently turn it into an inert rectangle.

What this tool does not do

• It cannot be undone in the file. The objects are gone and their appearances are page content now — the only way back is the copy you kept.
• It does not encrypt anything and does not stop the pages being changed by other means. Somebody with an editor can still paint over flattened text; what they cannot do is re-type a field.
• An answer with no printable appearance cannot be redrawn, and the notes say when that happened. It is rare, and it comes from forms written by software that leaves the drawing to the reader.
• XFA forms — the dynamic kind built for Adobe LiveCycle — are not flattened here. Their fields live outside the page model this works on.
• A digitally signed document loses its signature, because flattening rewrites the pages. The notes warn you when the file was signed.
• It has nothing to do with flattening layers or transparency. Optional content groups and transparency groups are left as they are.

What happens to your file

The file is uploaded because Flatten PDF runs on our server rather than in the browser tab. It is kept for at most 2 hours and the result you download for 24 hours, then a scheduled job deletes both — a job has to be able to read the file while it runs, and you have to be able to retry a failed conversion without re-uploading. Neither needs longer.

Nothing about the contents is logged, and no one reads your documents. The retention page lists the same numbers the code enforces, and the privacy policy says who can reach the storage they sit in.

Questions

Can I unflatten it afterwards?

Not from the flattened file. The fields no longer exist and their values are drawing instructions inside the page. The only route back is the editable copy you kept before running it.

Is flattening the same as protecting the document?

No. Flattening removes the mechanism that let somebody type in the field; protecting encrypts the file and sets permission flags. They answer different questions and are often used together — flatten, then protect.

Should I flatten the comments as well?

Only when they are meant to be part of the record. Flattened comments cannot be replied to, resolved or removed, which is right for a marked-up copy being filed and wrong for a draft still going round for review.

The signature on my PDF stopped working after flattening.

Flattening rewrote the pages, and a signature covers the exact bytes it was applied to. If the document has to stay signed, flatten before signing rather than after.

My form looks empty in the flattened copy.

The fields were probably empty in the file you uploaded. Some readers show typed values that have not been saved into the document — reopen your original and check that the answers are still there before uploading again.

Does flattening make the file smaller?

A little, sometimes: the annotation objects go away and their appearances become page content. It is not a compression tool, and a form with fifty fields will not shrink noticeably.