As you asked…
It appears that somehow your file pretends to be compliant to PDF/A.
Adobe decided to set an option by default to open documents claiming to be PDF/A compliant read-only.
You could suggest to your printer to go to the Acrobat preferences, into the Documents tab, and change the setting for Viep documents in PDF/A mode to "never", and that should do it.
On your side, you could check whether somehow you accidentially happened to save the document as PDF/A.
Hope this can help.