I allready fixed it!
It's a problem with dedicated GPU and MS Office hardware acceleration function. What you can do:
1. Try and make MS Office apps to run on built-in GPU. I couldn't do it — AMD Drivers automatically run it on dedicated GPU, ignoring my settings, I don't know why.
2. Disable hardware acceleration in any MS Office app settings. If you can't access settings ('cause you can't see any text), go to Control Panel — Power Settings — Change Power Scheme — Change Additional Parameters — Switchable GPUs and change it to 'forcible use built-in GPU' (naming may not be precise, I have another system language). Then launch any Office app (Word, for example), go to Settings — Advanced, scroll down about halfway, find something like 'Disable hardware acceleration' and tick the checkbox. Then you can revert your power scheme to previous settings, and every Office app should look normal when running on dedicated GPU.