If you are on Windows, follow these steps.
1. Upon downloading the PGN file, click open with and click the the box next to that bubble that says "browse".
2. Once you click "browse", click on notepad and hit "ok."
3. Hit ok again.
4. Copy all the text and use it anywhere on the forums, or just keep it in case you need to anylyse the game (optional).
5. Enjoy!!
If you are on mac, [no need to use expletives- - MOD] steve jobs cause i have no clue about his Mac [removed -- MOD]
He is clueless about Apple. He doesn't even know that Jobs died 5 years ago. (Tim Cook = CEO now.) 
Well, if you want a free, simple programe just to open PGN files, there are some of them in the Internet. I suggest you googling "free PGN viewer" or something like this.
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Just install WinBoard. It will associate PGN files to WinBoard during the install (unless you untick that), so that WinBoard will be automatically started in Game Viewer mode when you double-click the PGN file.
I have downloaded my games as a PGN file but I can't open it.
How do I find a programme that can open PGN files?