I'm a company director, and in India that means signing board resolutions and financial statements with a Digital Signature Certificate (DSC). The DSC is a Class 3 certificate on a USB token, the same one used for MCA and GST filings.

For a while, signing a PDF with that token meant paying for and installing a large commercial PDF suite. A lot of software for one click and a PIN. I wanted something small, free and offline that would never break a signature already on the PDF.

So I built TrackMy Sign , a free, open-source (MIT) desktop app for Windows, macOS and Linux. This post is about how it works underneath.…