This is something that drives me mad. Why (oh why) do word processors (Word, Open Office) paste formatted text by default? Almost always what you want to do is to paste unformatted text, so that it matches the font of the document you are pasting into, not the one you copied it from. Anyone who spends a lot of time filling in job application Word documents will feel the need for this.
After ages messing around with the infuriatingly complex OS X key re-mapping tool Karabiner, I found a way of doing it in Word itself. (These instructions relate to Word 2016 for Mac.)
First make a new macro in Word. Go to Tools > Macro > Macros… and make a new macro called PasteUnformatted.
Paste this code into the Visual Basic editor:
Then remap the cmd+V shortcut by going to Tools > Customize Keyboard… then pick ‘Macros’ from the Categories list. Find PasteUnformatted and assign cmd-V to it, click on the ‘assign’ button, and now every time you press cmd-V it should paste unformatted text that matches the formatting of the new document you are working on.
If you want to keep the option of pasting formatted text, assign a different, unused keyboard shortcut, but I am so convinced that unformatted is the thing you need 99.9% of the time, I’ve just replaced it.