I'm reviving the OP's tread, hoping that someone can help me with the same thing.
I can't find any way to attach files via a computer browser, Android Central app, or AC Forums app. –Well actually, I was finally able to upload a file via AC Forums app, but only after it prompted me to move to Chrome to do it.
When I downloaded the AC Forums app, via the suggestion in this thread, I found that a member had messenged me a week ago but I had never received a notification–and I didn't see one in the web browser interface.
Am I missing something here? I can't imagine that it's so difficult to attach files or receive messages, and I'm actually pretty tech savvy. Any help is very appreciated. Thanks!