Cannot modify or remove signature after doc was signed (Acrobat Reader DC)

[P5CF3]

I signed a form using Fill and Sign and saved the file. Now I cannot modify any of the fields or delete my signature. I was using Acrobat Reader DC. Before signing I had no problems modifying fields. Is there any way to undo a Fill and sign. Note, this was not a 'digital signature.'

[P5CF3]

This is very reproducible. Attached is the blank file which allows entries in all of the 'blue' fields.

The second file was signed and saved to disc. It will not allow any modifications and will not allow the user to delete the

signature.