Originally Posted by
Qwkynuf
This wasn't my request, but I would imagine that you would want .xls and .xlsx, maybe .doc and .docx.
A case could probably be made for including open source variants, such as .ods for spreadsheets and .odt for documents, but I don't know that it is actually necessary, given that every spreadsheet application that I am aware of can read and write to the MS format. The same is likely true for documents. However, the reverse is not necessarily true, and would potentially leave users of MS Office unable some files.
Just my 2 cents.
Certainly .xls & .xlsx. The things I've seen (and the one that I have) are spreadsheets, and I've mostly seen Excel, although there are likely Open Office variants as well.
Cheers.