Can UniPDF make a PDF uneditable?
Not completely, and neither can anything else. A PDF is a file the reader possesses, so anyone determined enough can alter the bytes. What you can do is remove the easy editing paths, restrict what a viewer offers, and make tampering detectable.
Which one you want depends on what you are actually protecting against.
| Goal | Use |
|---|---|
| Stop someone typing into form fields | Flatten the form |
| Discourage editing in a viewer | Encrypt with an owner password and restrict permissions |
| Prove the document has not changed since you signed it | Digital signature |
Flattening
Form fields and annotations hold editable content. Flattening draws them into the page itself, so the values become ordinary page content that a viewer offers no way to change.
This is the strongest of the three in practice, because it removes the editable objects rather than asking the viewer to hide them. See Flatten a form.
Permissions
Encrypting with an owner password lets you mark the document as not permitting modification, and a compliant viewer will grey out its editing tools.
That is enforcement by convention: the restriction is a flag a viewer chooses to honor, and a tool that ignores it can still edit the file. Treat it as a deterrent rather than a control. See Lock a PDF with a password.
Digital signatures
A signature does not prevent editing. It makes editing evident, which is often what people actually want when they ask for an uneditable PDF: the reader can verify the document has not changed since it was signed.
UniPDF supports the PAdES levels, including timestamping through a timestamp authority and long-term validation. See the signature guides, and Sign and timestamp a PDF for the timestamped case.
Signing and flattening interact, so do them in the right order: flatten first, then sign, since flattening after signing changes the document and invalidates the signature.