PDFs are perfect for the one thing they were designed for, which is publishing high quality proofs for printing. They aren't supposed to be editable. People just use them where they shouldn't.

How to sign a PDF.

1. Print the PDF onto paper.

2. Sign the paper version.

3. Scan the paper to a PDF.

Yeah, I know it's stupid but I did it 4 times this week for vendors. I do save some paper by getting a double sided scanner.

Internally all of my business activities use electronic signatures not in pdf's.

PDFs are great at one thing, which is creating a "digital printed copy", I.E something that will look the same on any device, and is pretty much universally supported.

Yeah... we really need to quit making proprietary formats into industry standards.

I always thought it made it look more legitimate and professional. Now I work with (somewhat) protected files, they're all just word documents haha.