Need to manipulate file metadata upon uploading from a cck form

Hi

I have a cck form in which there is a filefield for uploading any type of document file(doc, pdf, ppt, odt).

Now, I have to convert each kind of file to pdf file. i.e. when user click on submit, I want to process the file information before saving to db.

But, the problem is, I'm not able to find a place where I can put the code. I tried 'field_file_save($node, &$file) {', but upon changing I found that nothing changed in db. I checked my code, it worked fine. But, the information I put in $file data structure, is not being saved by DB.

Please help me.