To get a file virus, you need to run a copy of the infected file. To get a macro virus, all you need to do is double-click on an infected document, to view it. When it loads, its macros run, and you are infected. Because macro viruses are written in a macro language, a given macro virus will run in any environment which can understand and interpret those macro instructions. However, English versions of Word run in the Macintosh, in DOS, in Windows, in Windows 95, and Windows NT, so this virus can infect on all of these platforms.
Macro viruses are always application-specific.
Word Macro viruses will only infect Microsoft Word. A macro virus consists of a set of macros, nothing more. The macros must be stored wherever the application stores macros. In the case of Word, macros are stored in templates, rather than documents. Word treats any file with the .DOT extension as a template, and any other extension as a document.