A document can only be opened and signed with the link in the email.
Use the link in the email to start signing the document. This is done in your web browser.
If you receive a document with “Advanced Electronic Signature (FES)”, a pin code will be sent to you via SMS before you can open the document.
You can view the document here.
The places where you need to sign and possibly provide further information can be seen as fields on the document.