I use Libreoffice at work to open and edit MS Office files and it works mostly fine, except for PowerPoint (missing fonts but also general madness). In general,

I use Libreoffice at work to open and edit MS Office files and it works mostly fine, except for PowerPoint (missing fonts but also general madness). In general, I think the LibreOffice folks did a great job, esp. when it comes to MS file format support. And of course they need to, because I (and I guess most people) actually open more Ms files with LibreOffice than files in LOs native formats.