To produce an html page for fopen do:
man fopen | man2html > fopen.html
The source may be found here. It seems to be ISO C. I compile it with
gcc -Wall -o man2html man2html.c
man fopen | ./man2html > fopen.html
It has been tested a little in x86 Linux and Solaris. This code must have been written many times.
Subsequently to writing this code I found another program by the same name that has many nice options, but it is 45KB. AltaVista knows others.