Why does saving a Writer Document remove signatures?

After finally getting LibreOffice to find my digital certificates by starting it via Terminal (please fix that already), I digitally signed my document.

Then I wanted to save it and got:

Saving will remove all existing
signatures. Do you want to continue
saving the document?

Why? Why does this happen? What logic am I missing? What is the purpose of not being able to save a document WITH a digital signature attached to it?

Just consider it’s not only you who could modify a document - thus you won’t be happy, if anybody could change your file and legally bind you to pay an arbitrary amount of money (or any other obligation) based on a document digitally signed by you. As with real paper, you need to sign a changed and legally binding document again.

The confusion might arise from the not obvious fact that signing saves the document itself. Thinking that signing is just another modifying operation on a document, after which the document needs to be saved, and seeing the warning, may confuse users - I suppose some improvement in workflow is needed, like a clear message after successful signing that the file has been signed and saved, and possibly turned into read-only mode…

@anon73440385 is right.

For obvious reasons you don’t want a signed document to be modified. Your signature is going to be automatically saved. You can just close the document without saving it, reopen it, and see that the digital signature is still there.