How can I open up a .pdf or other file (like .txt, .doc or .docx) in a C program?

I am writing a C program for a voice recognition development board. Once the program recognizes me as saying something I want a specific file to be opened. Is there a way that I can have a file opened up in C code? Obviously it will be opened up in its respective program. Once it reaches a specific "if" and evaluates it as true, I want this file opened up. Examples include: .txt, .doc or .docx I have a 64-bit Dell running Windows 7 OS.

The easiest way is to capitalize on window's existing file associations using the WinAPI ShellExecute() function. That would let you simply send the filename to the function and it would open in it's pre-associated program.