You mean the part you're stuck on is where you upload the file from a client machine back to the server? Your question could use some clarification, and you could show us the code you're actually working on/having problems with, How do I post a question effectively?.

Thanks for the reply. there are three steps : 1. upload a file from my machine ( client ) to server machine using CGI -> i am done with this part. 2. convert the uploaded file to the required format -> i am done with this part too. 3. Now the converted file is under some dir of server machine , now i want to get ( downlaod ) this file back to may local machine ( client ) -> i am stuck in this part.

One solution would be to load the file contents into memory and serve the content with the appropriate header. This of course depends on the size of the file, you don't want to load large files into memory and serve it like this. You could copy the file into a temporary web accessable area and provide a link to it.

Other things to consider, do you want to remove the converted file after you've sered it, so that you don't end up filling some filesystem with old files people have downloaded? Perhaps you'd need to write a housekeeping script to tidy up these files/areas on a regular basis. Clarify your requirements and consider the implications of your system. See also Print to Browser Headers Not Working Serve a file from a CGI script.