There are 2 repositories under pdf-signer topic.
Free web software for signing PDFs and also organize pages, edit medata and compress pdf
A tool to sign PDF files. With Linux support.
📑 HTML5 Javascript Online Offline Browser Editor 📜 for PDF files for insert sign, images, photos, comments or annotations
Digitally sign PDF document from your phone using handwritten signature or image.
:lock_with_ink_pen: Sign PDFs with the portuguese citizen card (aka "cartão de cidadão")
Windows executable for sign a PDF with a certificate and a hanwritten signature
Firma massiva in formato PADES usando una smartcard
Google KSM Signer implementation for pyHanko