If you’re using your computer for work and can’t afford to spend some time figuring out how to do something that would be second nature for you on Windows, you shouldn’t switch. It would probably be more expensive than just buying a Windows license.
That said, you shouldn’t expect too many problems. You can try out your Word templates right now in Libre Office. Or just run the web version of Microsoft Office in Linux. Video codecs are usually just one command away.
In terms of what distribution to choose, I would choose something popular that’s stable and comes with sane defaults. Debian, Ubuntu, Fedora or OpenSUSE Leap.
The main difference for a newbie will probably be how to install software. On Linux you usually don’t go to the manufacturers website and download an installer. Instead you go to your software center and search there for what you need. Similar to the App Store and Play Store on phones.