Delete signature in pdf really possible?

I added a signature to a pdf file on my iPad (Files App -> Markup -> + -> Signature) and closed the document. When opening the pdf on my iPad I cannot remove the signature anymore. I then forwarded the pdf to a windows pc and when opening the pdf with Pdf-XChange Editor I was able to select and remove the signature. Why is that? I was under the impression that this should not be possible. How do I sign a pdf so the signature cannot be removed anymore?

Thanks.

edit: furthermore I can select the signature and save it as a png file (on the windows pc)

edit2: I also tried to lock the pdf. This only lets me create a password to open the file. Once opened the signature can be removed still.