Fuzzy speaks in his best SGT Sparky voice: "yes they can! now play my latest game and tell me what you think!"
You'll want to study fread, fwrite, fgets, fputs, and especially fgetc and fputc. to open files you will need fopen() and fclose(). once you understand them, go and study a simple file format like tga. There are lots of references to the format on the web.
Here is some definative reading:
http://en.wikipedia.org/wiki/Fopen