So basically you want to write your own conversion software in PHP to convert PDF files to text and post it to mysql.... Like most programming ideas it sounds easy but is probably going to take a while to code. I suggest you look into the format used for storing PDF files and you will see why others have been suggesting software to convert the file for you and then post the results to the database.
Why don't you just store the file in a folder and store the filename in a db? I tend to think of it as files go to the filesystem and data goes to the DB. You could end up with a huge amount of data in a table that could become unwieldy by storing files in blob fields. But there may be situations where this is preferrable. How many files are we talking about? Size?