Client got a letter from MonoType—don't even know if it's our fault.

We have a client that is in the $100's of millions in size. They have several brands, websites, and agencies working for them. MonoType emailed the client about an unlicensed font. Now they are they are getting all their agencies audit fonts use in all pieces.

I do have a few question in response to this:

If a PDF is provided as a download, my assumption that a desktop license held by the document designer is good as long as the content is no editable. I'm being asked to audit PDFs, so I'm curious. I know laws are not the same everywhere. The client and I are in the US, but I am interested in hearing perspective from other regions.

Other question I have is, when MonoType sends a letter, do they say what font is in violation and where it is being used. The impression I'm getting is the our agency may or may not be a fault and we are being asked to produce evidence of our error. I don't believe we have done anything, but it's still difficult not to feel guilty.

The good news is this is billable work for the art department. If account services has to write the time off because they cannot bill the client it, that is not my problem. Preventing the client from chasing our own tail is a big part account services responsibility.