In case you're still confused, Khandro, (and temporarily ignoring what your question's actually about just for the moment) . . .
Once you've highlighted text in a Windows-based program, there are three ways of copying it to your clipboard:
1. Go to Edit > Copy ;
2. Press Ctrl and C together ; or
3. Right-click on it and select 'Copy'.
Similarly, once you've clicked where you want text to appear, there are three ways of pasting it:
1. Go to Edit > Paste ;
2. Press Ctrl and V together ; or
3. Right-click on it and select 'Paste'
You can 'mix and match' those methods if you want to. (e.g. you could use 'Method 1' for copying but follow it with 'Method 3' for pasting).
To return to your question:
My first suggestion (in my original post, above) was to try 'Method 2' for pasting but to modify it by pressing Shift as well as both Ctrl and V. In some programs that pastes without formatting.
My second suggestion (above) was to paste as you usually do (thus gaining the unwanted formatting) but to then highlight the text which has appeared in the wrong font and press Ctrl and Space together. (Again, that works in some programs but not all).
My final suggestion (above) should definitely work though. You simply set up PureText to run automatically as soon as you start your computer and then choose a hot key combination (such as the Windows key and V together, or anything else you choose) to use as an alternative to 'Method 2' above.