Type on any form, tick the boxes, add your signature and initials, stamp it and save a signed copy. Your original is never changed.
Save a form you fill every week - where the text, signature, date and stamp go - then fill it again from a few questions, or make a copy for every row of a spreadsheet.
Put your signature, initials, date or stamp on the open PDF, then add the same marks in the same place on a whole stack of PDFs - a week of timesheets or delivery notes in one go.
Marks keep their distance from the nearest corner, so they land in the same place on A4, A3 or letter.
Every signed copy you've saved on this computer: when, which document, what was added and whether it carries a certificate signature.