This is basically correct. A court will generally accept a writing into evidence as long as it is relevant and authenticated by a witness or certification.

I had the case where one person was signing PDF using the annotate / drawing feature. Didn't work in court, the court claimed the contract was invalid (it was the situation of a founder of a company that was raising on a convertible debt).

That sounds totally absurd. Unless the stipulation was instead for a wet ink signature I just don't see how this could be the case.

You can enter into a contract with even less than a signature (ie: just by accepting payment you can inadvertently end up in a contract), so the idea that a signature wouldn't work except in very specific cases seems pretty weird to me.

I've had very few wet-ink, notarized signatures required of me. Some documents are weird though ie: a picture won't be accepted, but a scan will be, etc.

God it's all so fucking stupid.

Can you share the Pacer link?