I just create a Document item and attached a 53MB PDF file. The application did allow me do that, however the item was hanging in the "Offline changes" view forever. Then I tried to remove the item, which also did not work, so I reset my local data and started over.
When I try to upload the same PDF in the web application, I am warned that there's a 50MB file size limit.
Having this hint in the Windows application would have saved me some time
1Password Version: 7.3.705
Extension Version: Not Provided
OS Version: Not Provided
Sync Type: 1Password.eu