Three levels that get mixed up
Anyone wanting to sign a PDF meets three very different things, all called a signature.
The signature image. You draw your signature, photograph it or sign on a trackpad, and the image is placed into the PDF. Legally this is a simple electronic signature.
The advanced signature. It is tied to a certificate and shows whether the document was altered after signing.
The qualified signature. It comes from an accredited trust service provider and requires an identity check. Under EU law only this one replaces a handwritten signature on paper.
What is actually needed day to day
For most documents the first level is enough. Order confirmations, quotes, registrations, a signed cover letter in a job application: nobody here wants to prove anything in court, they simply want to see that you agreed. Sign PDF places your signature where it belongs and gives the document back.
When a simple signature is not enough
For contracts with a statutory written form requirement. In Germany that includes terminating an employment contract, guarantee declarations and consumer loan agreements. There, paper or a qualified signature is the only way. A tenancy agreement running longer than a year also requires written form.
One practical note
Once a signature is in place, the document should not be edited further. It makes sense to lock the pages afterwards with flatten, so form fields and annotations sit firmly in the document and cannot shift on the recipient's machine.
How the signature gets into the document
There are three usual routes. You draw with a mouse or trackpad, which on a laptop tends to look scrawled. You sign a sheet of paper, photograph it and upload the image, which gives the cleanest result. Or you type your name and pick a script font, which is practical but visibly not your handwriting.
For a cover letter or an order confirmation the photograph is the best route. Shoot in daylight on white paper, then the background can be removed cleanly and the signature later sits on the document without a grey box around it.
Where the signature belongs
Above the typed name line, not below it and not across it. In contracts between two parties the signature fields usually sit side by side, the provider on the left, the customer on the right. Place and date go before them, and the date should be the day it was actually signed.
Common questions
Is an inserted signature forgery proof? No, and that is not its purpose. An image can be copied. Where evidential weight matters, only a qualified signature will do.
Can the recipient tell it was signed afterwards? Not reliably with the simple variant. That is precisely what the advanced signature is for, it makes any later change visible.
Is a scan of the signed page enough? For everyday purposes yes. Legally it sits at the same level as the inserted signature, namely a simple electronic signature.
What about cancelling my phone contract? In Germany text form has been sufficient since 2022, so an email will do. Resigning from a job is different: that requires paper with a handwritten signature. A suitable termination letter can be prepared and then printed.
Before you send
Open the finished PDF in a different program from the one you signed in. Annotation layers occasionally show only in your own viewer and go missing for the recipient. To be safe, lock the layers with flatten.