But i had read a comment in this forum only that we can write .pdf files onto CD, but first we have to convert it to .iso file through NERO.[/QUOTE]You do not convert the PDF (DOC, XLS whatever) to ISO.
.ISO is just an image file of a disc.
Your burning application should be able to put all files of a given compilation into either such an image file, or burn directly to disc.
Mkisofs is a very widespread tool to create .ISO images from file collections. There is also a Windows version and Source Code available. I am not a programmer, but I thought mkisofs might be helpful for your purpose.