If you want help, be specific:
What type of attachments are you downloading?
How does it "convert" them into text? Does the file extension change, or does the binary file actually change to text so that it is unopenable even when the correct file extension is restored?
I can think of several reasons why attachments could have problems, but I would be speculating since you provided no detail. Add some detail and perhaps that will lead to a better understanding of what could be occurring.
I am not WHB staff and I am not paid.
I provide help in these forums on my own time.