This PHP Script has an Anti-Leech feature turned on.

Make sure you are accessing this file directly from www.steam-brite.com

It seems you are trying to get it from https://steam-brite.com/literature/schematics/index.php?dir=Powrflite%2FSchematics%2F&file=SD800.pdf

Your IP address has been logged.
18.119.127.13 (ec2-18-119-127-13.us-east-2.compute.amazonaws.com)

Here is a link to the directory index the file is in:
http://www.steam-brite.com/literature/schematics/index.php?dir=Powrflite/Schematics/