Hey there! Thank you for reaching out here. This article is super handy regarding which files are supported when adding attachments: https://www.xfinity.com/support/articles/trouble-sending-file-attachments. Let us know if this helps!
You didn't answer the question. The problem is with your app, (e.g., iOS, Galaxy, Android) not OS (i.e. MS Windows). On iOS I can only attached a photo. I need to attached pdf from iPhone and iPad.