Разбира се, ето един възможен превод на английски на твоя имейл, който звучи професионално и ясно излага проблема:

Dear [Име на получателя],

I am writing to report an issue I am having with adding comments to a shared PDF file. The file owner sent me a link as usual, but this time I am unable to post comments on the file.

The message I am receiving is "Comments can't be added / This file is shared for viewing only. If you want to add comments or annotations, create a copy." The file owner assures me that they shared the link with the same settings as always, which have worked fine for previous files they've sent me.

What's strange is that when I log out of my account, I can post comments as a Guest. However, once I log back in with my own account, the option disappears.

I would appreciate it if you could investigate this issue and provide me with your findings. If necessary, I can provide you with a link to the file.

Thank you for your assistance.