Update
php cannot easily access hardware. This is generally not considered "possible."
See:
However, as the first link shows, this is usually done with Javascript. You can output Javascript in a way similar to the methods shown on the first link to force the browser to show the print dialog box.
Original
You can use file_get_contents to print files into a variable or to the output stream.
$filecontents = file_get_contents("myfilename.txt");
print $filecontents;
You can also include files into your PHP interpretation.
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