LibreOffice lets you sign digitally a signature line in your document.
On signing a signature line, LibreOffice fills the line with the name of signer, adds the digital certificate issuer information and optionally insert the date of signature.
Select the signature line graphic object context menu. Choose Sign Signature Line.
Enter your name as signer of the document. Your name will be inserted above the signature horizontal line.
Click on the Select Certificate button to open the Select Certificate dialogue box, where your certificates are listed. Select the certificate suitable for signing the document.
The information of the certificate issuer is inserted in the bottom of the Signature Line object.
This area displays the instructions entered by the document creator when adding the signature line.
Enter comments about the signature. The comments are displayed in the Description field of the certificate.
If enabled when the signature line was created, the date of signature is inserted on the top right of the signature line object.