Not sure which version of Office you have at the moment, or which OS is currently on your computer.
I myself am still using Office 2007 on my 11-year-old desktop computer which was running XP but has now been upgraded to Windows 7. I also have a laptop which has been upgraded to Windows 10 and I purchased a copy of Office 2013 for that - and I regularly swap Word files from one computer to the other without there being any problem.
The following link leads to a chart which tells you which versions of Office are compatible with Windows 10 (assuming you are getting a Windows 10 laptop): - http://www.keynotesu...ity-chart.shtml
I am not exactly sure what you mean by: 'Should I even trust a used MS office copy'. Do you mean the one previously used by you, or another one? You should be able to load any undamaged copy of a compatible version of Office - but bear in mind that you will have to enter the Microsoft Product Key, so you will need to have that to hand.
You may actually be able to download a digital copy of a previous version of Office free from the Microsoft website; the Product key is the most important part!
Hope this helps,
Edited by Channeal, 02 June 2017 - 06:57 AM.