Apply Digital Certificate (.p12) to PDF Programmatically

I need a developer with experience in digital signatures and PDF processing to help me apply a .p12 (PKCS#12) digital certificate to PDFs in my workflow.

The goal is to take an existing PDF file, apply a digital signature using my .p12 certificate, and output a valid, signed PDF that can be verified in Adobe Acrobat and other PDF readers.

The PDFs involved may contain dozens of pages, so performance across multi-page files matters. At minimum the code should:
• load an external .p12 (PKCS#12) file and apply the certificate,
• save or stream the newly signed PDF without corrupting any existing content or bookmarks.
-Achive the signature banner that shows this document has been digitally signed by a CA authority.

Requirements:

Experience with PDF digital signing (preferably using Python, Node.js, or another modern language).

Familiarity with PKCS#12 (.p12) certificates and private key handling.

Ability to ensure the signed PDF passes validation (byte ranges, integrity checks, timestamp if needed).

Deliver a working script or utility I can run via NVite + React + Supabase (Typescript)


Deliverables:

A script or small program that takes:

Input PDF file

My .p12 certificate + password

Outputs a digitally signed PDF

I already have all of the integration pieces and will share source via GIT.