How do you sign a secured PDF document?
Written by Cameron James·September 4, 2026Quick answer
Start by working out which lock is on the file. If the PDF simply asks for a password before it will open, type it in and sign as you normally would. If it opens fine but the signature and Fill and Sign tools are greyed out, the sender has applied a permissions password that blocks changes, and the clean fix is to ask them for a copy without that restriction rather than trying to strip the security at your end.
Key facts
- PDFs can carry two separate passwords. A Document Open password controls who can view the file at all. A permissions password lets anyone open it but restricts actions such as editing, printing and copying.
- Greyed-out signing tools on a file that opened without a prompt almost always mean a permissions password, not a broken install.
- Acrobat's permission settings are granular enough that a sender can block general editing while still allowing form filling and signing of existing signature fields. If yours are blocked, that was a choice someone made.
- A certifying signature already on the document can disallow any further changes. Adding your own signature on top will either fail or flag the earlier one as invalid.
- Print-to-PDF and re-save workarounds do get you a signable copy, but they flatten the file. Form fields, existing digital signatures and any embedded interactivity are lost, and what you sign is technically a different document from the one you were sent.
- Removing protection you were never given the password for is circumvention, and in a contract context it is the kind of thing that gets raised later. Ask the sender.
- If the document exists to be signed, an e-signature service handles it properly. A locked PDF forwarded round by email is the wrong tool for a signature workflow.
Which lock are you actually looking at
Two different things get called a secured PDF and they need opposite responses. One asks for a password the moment you double-click it, which is a Document Open password, and the answer is simply to get that password from whoever sent it. The other opens straight into the document and only shows its teeth when you reach for the signature tool, which is a permissions password sitting on top of an otherwise readable file. Check Document Properties and look at the Security tab if you want to see exactly what has been switched off.
Why the signing tools go grey
Acrobat's permission settings are finer-grained than most people realise, and one of the options a sender can leave open is filling in form fields and signing existing signature fields while everything else stays locked. So a greyed-out Fill and Sign is usually somebody ticking the wrong box on the way out, not a deliberate refusal. Print-to-PDF workarounds do get you a signable copy, and I understand the temptation when a deal is waiting, but they flatten the file: form fields go, any existing digital signature goes with them, and you end up signing a document that is not quite the one you were sent. On anything that matters, one message asking for an unrestricted version costs you almost nothing and saves the argument.
If the lock was about control, not signing
Worth separating the two problems, because they get conflated constantly. Password permissions are a poor way to stop a document being forwarded, given how easily a print-to-PDF undoes them, and that is usually the real worry behind a locked file. Sharing through a link you can expire or revoke does that job properly, which is part of what LiveDocument handles alongside the video walkthrough and the page-level analytics. To be clear about what it is not: it does no signing, no watermarking and no NDA gating, so for the signature itself you want Acrobat Sign or DocuSign, and for watermarking DocSend is the honest pointer.
The Bottom Line
Most of the time a secured PDF you cannot sign is not a technical problem you need to solve, it is a permissions setting the sender left switched on by accident. One message asking for an unrestricted copy will fix it faster than any workaround, and it leaves you with a document that still holds up.
Written by Cameron James