mutool sign

The sign command reads an input PDF file and by default prints information about each signature field object. The command applies to the signature field objects given, or every signature field if none are specified. Given suitable option signature fields can be verified, cleared or signed using a given certificate and certificate password.

mutool sign [options] input.pdf [signature object numbers]

The options are:

-p password

Use the specified password if the file is encrypted.

-v

Verify each signature field and check whether the document has changed since signing.

-c

Revert each signed signature field back to its unsigned state.

-s certificate file

Sign each signature field with the certificate in the given file.

-P certificate password

The password used together with the certificate to sign a signature field.

-o filename

Output PDF file name.

input.pdf

The input PDF document.

signature object numbers

Can be used to specify a particular set of signature field objects to apply the sign command to.

Signing

Signing digital signatures in MuPDF requires that you have a PFX certificate. You can create a self-signed certificate using OpenSSL by following these steps:

1. Generate a self-signed certificate and private key:

   openssl req -x509 -days 365 -newkey rsa:2048 -keyout cert.pem -out cert.pem
   

2. Convert to PFX format:

   openssl pkcs12 -export -in cert.pem -out cert.pfx
   

Examples

The following command should show all signature fields in the PDF whether signed or unsigned:

mutool sign -v unsigned.pdf

Once you know the object number of an unsigned signature field, then do the following:

mutool sign -s certificate.pfx -P password123 -o signed.pdf unsigned.pdf 4242

This assumes that object 4242 0 R is the signature field. Re-running mutool sign -v signed.pdf should then show that the signature was signed.

To clear a signature use the -c option:

mutool sign -c -o unsigned.pdf signed.pdf 4242