more precisely echo sends text, but if its html code, and the person/thing receiving it is capable of displaying html, it will show up as a webpage.
if the program writes the page to a file, then [man]file_get_contents[/man] might be what you will want to use to show the page.
also, depending on how complex this program is, you could get php to do the same thing without the additional overhead of calling an external program.
is there any relevant code you have already that could help me understand what you are doing?