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Create sample Microsoft Word document with invalid electronic signature

I’m involved in informal education of notaries public. I would like to create a sample Microsoft Word document with a valid electronic signature, made with a digital certificate. I would then like to alter the document so the signature becomes invalid. I could then show the students what a document with an invalid signature because of tampering looks like.

If I try to do this with Word, it makes me click an “Edit anyway” box and removes the electronic signature as soon as I click. If I edit with Notepad, the document becomes corrupt and I can’t load it.