(This should be in the Sony subforum, not in the Workshop forum. Maybe a moderator can move it.)
Didn't your Sony come with library software? Use it to send files to and from your reader.
Or if you'll mainly use it with free books downloaded online, then you can use
calibre.
Don't worry too much though. If you copy the file over the reader directly, the reader will find almost anywhere you put it, and unless you start deleting stuff other than your books, you won't do any harm.