they are data files associated with different programs - docx is the new
Word document format, RTF is an older generic word format and HTML is a
format used in browsers.
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Diane Poremsky [MVP - Outlook]
EMO - a weekly newsletter about Outlook and Exchange:
(e-mail address removed)
They're just more file formats (how the data is structured inside the
file). There are also .txt, .bmp, .pdf, .xls, and lots of other file
formats. If you want to see a whole bunch of different filetypes, go
visit www.filext.com. They have over 50,000 different filetypes listed.