Electronic signatures and digital signatures
One is a picture of your name on the page. The other is a cryptographic seal over the whole document. They solve different problems and the same word is used for both.
What is an electronic signature?
Any mark you place on a document to show that you agree with it: a drawn line, a typed name in a script face, a photograph of a wet signature. It is a picture on the page, and it carries as much weight as the process around it gives it.
That is often enough. For internal approvals, delivery notes and most everyday agreements, a signature plus an email trail is what both sides actually rely on, and adding cryptography changes nothing about the agreement itself.
What does a digital signature add?
Proof that the file has not changed since it was signed. A certificate signature computes a cryptographic hash over the whole document and seals it with a private key, so any later edit invalidates the seal and a reader will say so.
It also binds the signature to whoever holds the certificate. A drawn signature can be lifted out of one document and pasted into another in a minute; a certificate signature cannot, because it is computed over the bytes of one specific file.
Which one do I need?
Ask what would go wrong if the document were altered after signing. If the answer is nothing much, a drawn signature is proportionate. If the answer involves money, a regulator or a court, you need the seal, and you need a certificate that somebody will accept.
Being accepted is the harder half. A self-signed certificate is cryptographically identical to a purchased one and every reader will flag it as untrusted, so it is right for internal use and wrong for anything that leaves your organization.
What about qualified signatures?
That is a further step, where a supervised provider verifies your identity and issues a certificate on a secure device. In the European Union it is the only form the law treats as equivalent to a handwritten signature, and it involves an identity check no software can perform on your behalf.
This suite issues no certificates and performs no identity checks. It signs with a certificate you already hold, which is the right tool once you have one and no help at all in getting one.
Where to go from here
Sign a PDF places a drawn, typed or uploaded signature on the page, signing with a certificate seals the document with a certificate you supply, and protecting the file is what stops it being opened by anyone without the password.
PDF forms explained covers the field a signature usually sits in, and PDF/A and long-term archiving explains what happens to a signature years later.