Answer by Cpt.Whale for Create sample Microsoft Word document with invalid electronic signature

These steps will work in Windows. I'll just use example folder paths:

1. Create a document with some sample text like TRUE to search for, and sign it
2. Copy your valid signed word document to C:\temp\valid.docx
3. Rename the file to test.zip (you may have to enable viewing file extensions)
4. Right-click the file > Extract All... > Extract. This should create a folder named valid
5. Open the file C:\temp\valid\word\document.xml in notepad
6. Edit some of the sample text (TRUE -> FALSE), save, and close the xml file
7. Select everything inside the C:\temp\valid\ folder (you should see folders named _rels and word for example).
8. Right-click > Send to > Compressed (zipped) folder
9. Rename the zip file to edited.docx

When you open edited.docx in Word, the document will not be corrupted, you'll see the edited text, and you should get a notification showing invalid signatures

Older .doc files and such work the same, but have slightly different internal file names