Don't waste your time looking for a deep dive PDF. The "Acer MG43M Manual" is a mirage. Instead, look for community forums about the Acer Aspire XC-600 or T3-715 —those are the computers that actually house this board.
Spoiler alert: You aren't going to find it.
If you are reading this, you have likely just picked up a used Acer Aspire desktop, or you are trying to resurrect a dusty tower from the back of your office closet. Inside, you spotted the model number MG43M printed on the green PCB.
This means Acer never intended for you to upgrade it. They intended for you to call their tech support if it broke.
You have the proprietary PSU that fits it (Acer often uses non-standard 12-pin power). Replace it if: You want to use a standard case, standard fans, or overclocking.