E_ADEPT_DOCUMENT_TYPE_UNKNOWN for a .acsm file pointing to a PDF of ebook

I bought an eBook from Google Books. When I try to open the .acsm file in Adobe Digital Editions 4.5 (on an Apple OS X 10.9.5 system), the one for the .epub downloads fine, but the one for the PDF version gives me this error:

Unable to download

Error getting License. License Server Communication Problem:

E_ADEPT_DOCUMENT_TYPE_UNKNOWN:

   how to get past this?