I understand. What I used was a pentablet to write. Smoothdraw is the app i’m using as the canvas. I just painted it with black so that’s it’s easy to look at (vs a white background).
For the recording part, i use bandicam. Im using a Windows OS.
With regards to your question about PDF files, I can’t recall if I have seen any video using that. A powerpoint presentation, there’s a lot.
Personally, PDF files, i use them when I practice (for example if when I want to do sample problems with balancing or something
If you have more questions, I would love to hear them.