Digitally Sign a PDF

 Use digital signatures to verify the identity of the signer and protect the document content. A digital signature confirms that the document has not changed after signing.

When a document is digitally signed, Nitro PDF Pro restricts some actions to preserve the document state.

Digital IDs or certificates can support legal validation.

To digitally sign a PDF

1. On the Protect tab, in the Certify Document group, click Sign
2. Select a signature from the gallery
   1. You must have a digital ID to sign a document
3. Click the location on the page where you want to place the signature
4. Review the signature details
5. Save the PDF

Document behavior after signing

After you sign a document:

• Some actions are restricted
• The document state is preserved
• The signature can be validated when the document is opened

Edit a signed document

• If you are the only signer, you can remove your signature and edit the document
• If other users have signed the document, request an unsigned copy from the sender

To remove a digital signature

1. Right-click the signature
2. Click Clear Signature Field
   

To lock a document after signing

Use this option to prevent all changes after the final signature.

1. Add a digital signature
2. Select Lock document after signing (if available)
3. Save the PDF

When you lock the document:

• The document becomes read-only
• Users cannot edit, comment, fill forms, or add signatures

Use this option only if no additional signatures are required.

If the document is locked

• You cannot add more signatures
• To add signatures, all signatures must be removed and added again without locking the document

To unlock a document

Only the final signer can unlock the document.

1. Right-click the signature
2. Click Clear Signature Field
   

Additional information

• To sign a document, you must have a digital ID
• To lock a document without a signature, use the Certify feature
• The Audit Trail shows when a document is locked after signing