thanks guys, for giving advice. I think calibre is the best tool for me. I can sort using its tags easily now and it's really awesome
btw, what software you guys use if need editing to read downloaded PDF on your PRS-700 model ? I use PDFCropper and so far it's awesome. I just want to cut out the unnecessary portions like margins and whitespace to make texts bigger on the reader and so, that program suits my purpose.