I recently had a similar issue, not a PDF attachment, it was a .html document that was dragged & dropped to Evernote App on Mac - it seems there was something special inside that code that prevented from syncing -Mypascoconnectdid a copy & paste instead (not sure if I was using the texteditor as a intermediate step) to get the contect into my Evernote space.
Since I was in hurry I did not do any further investigation...
PDF attachment failed to sync, I'm going crazy
in Evernote General Discussions
Posted
Thank you for the information and advice!