how to uncompress a file ending with diff.gz
 

I managed to uncompress the gz part, but I still have a diff ending. what do i do?

What exactly are you trying to do?

the full story
I have a file that's suposed to contain the functions "xwdtoppm" and "ppmtogif". I downloaded it , it's name is:
netpbm-10.0-10.1.diff.gz
when I use gunzip, i get an exacutable file with the same name without the gz (ending with diff). I do not get the two functions. one of them (xwdtoppm) is not recognized.
I thought that the uncompression was incomplete. am I mistaking?
I know that the full file should be bigger than 1.5M, but the file ending with diff (after the gunzip) is only 38k.

thanks again.

You have downloaded a "diff" file. The file contains the DIFFerence between two versions of the same source file. You need to use the utility "patch" and apply this diff to the source code.

Regards