How to flatten a PDF form so it can't be changed

Flattening a form in PDF by Zaweba is done with its Flatten command, which draws the form fields into the page and removes them as live objects. The answers stay visible exactly as they were, but nobody can click into a box and change them. The same command can flatten comments too, and the app is free and works offline on Windows.

It's the step to take before you file, archive or send a completed form that should be read rather than edited.

What flattening does

A fillable form has two layers in a sense. There is the page itself, with its printed text and lines, and on top of it there are fields, which are interactive objects holding the typed answers. A PDF reader shows the fields over the page and lets you change them.

Flattening merges the two. The look of each field, with its current answer, is drawn into the page, and the field object is removed. What you see doesn't change. What you can do with it does.

Flattening a filled form

Open the filled form in PDF by Zaweba and check the answers first, because once a form is flattened, the fields are gone. If you might need the data later, export it before you flatten. The app saves field values as XFDF, FDF, XML, CSV or tab-separated text.

Then run Flatten for the form fields. Look over each page to make sure everything looks right, and save. A good habit is to use Save as and keep both versions: the live form for any corrections, and the flattened copy to send.

Fill and sign items and comments

If you filled in a flat form with Form, Fill and sign (typing text, adding the date, ticks or your signature), those items stay as separate annotations until flattened. Saving flattens them by default, a setting you can change, and flattened text becomes real text in the page. There's also Flatten fill and sign, which flattens only Fill and sign items and leaves other comments as they are. That's useful when a document carries review comments you want to keep live.

The same idea applies to comments. Highlights, notes, stamps and drawings are annotations that sit above the page. Flattening comments draws them into the page and removes them as annotations, so they print reliably and can't be moved or deleted by the next reader.

Mistakes to avoid

Flattening isn't the same as hiding information. If a field held something private, flattening keeps it visible on the page. To remove content properly, use redaction, which takes the text and picture pixels under the marks out of the file.

Nor is it the same as protection. A flattened page is still an ordinary PDF page. If you need to stop changes, add a permissions password, or sign the document with a digital ID so any later change shows up.

Don't flatten the only copy of a form you may need to reuse. Keep the blank original, and if you want to fill it in again, use Form, Clear form on an unflattened copy instead.

Doing a batch at once

Flattening one file by hand is quick, but a pile of returned forms is better done together. Tools, Actions are saved lists of steps that can include flattening alongside removing hidden information, reducing size or protecting, and they run on files, a folder or the open document. Set one up once in PDF by Zaweba and a whole folder of completed forms can be flattened in a single pass, ready to archive.