On a question I recently asked regarding passwords on PDFs, a comment was made that the OS should be included in the description and a tag for it used. When is it a good idea to include the OS? It seems like any question involving a file, format or program could somehow be related to an OS. For example if a question is about using Word 2013 is it necessary to tag it Windows? What if it's about the way Word saves its files?
In the PDF situation, it doesn't really matter what OS is used to accomplish the task so I thought specifying one would be unneeded. For example I have access to Windows 7, 8 and Ubuntu so should I use all the tags?