converting word document to plain text file

hi, i need to store some files that contain text in my database. im planing to upload the file using a php script. what id like is to be able to take the info(text writen in the file) from the file and store it on a plain text file and then store it since i plan to consult the info in these plain text files later. the thing is that in case someone decides to upload a *.doc, *.rtf or *.pdf, i dont know how to read such files to get the text from them. is there a way to these types of files in php or some other way? thanx.