Yes you can however Moon copies the files over to an internal Moon directory, so you will have two copies of that file. Also Moon reads several formats (ePUB, txt,html, FB2,etc..) but it does not read MOBI/AZW.
Montago is a new reader that is very nice and reads ePUB/PDF. It does not move files round and will use the original file location. This app is a paid only app.