I am running High Sierra on a Late 2011 MacBook Pro. I have Mountain Lion on an external drive with Microsoft Office 2008 installed. Office works normally on Mountain Lion but won't install on High Sierra, probably because it is a 32 bit app. However when I plug in the Mountain Lion external disk, 2008 for Mac Office seems to run just fine under High Sierra. I did not have much luck migrating Word from the Mountain Lion hard drive to the High Sierra disk but Excel seems to have migrated OK. Would be interested in any experiences others have.