I use a lot of presentations that were originally created in M$ Powerpoint, that I download from Baidu Wenku. Sometimes they work fine in LibreOffice, and don't have to change anything. but often there are formatting issues that have to be fixed. It's usually when they contain Chinese characters, or an image might be misplaced and is obscuring the text. It's not really a big problem for me now, because I'm always making changes to them anyway, to make them suitable for my lessons. And then I save them as .ODP, the native format.
I'd rather do this because I prefer not to be using Micro$oft products these days, if I can avoid it. Think I've come to detest Micro$oft almost as much as Moody now.