The change from .xls to .xlsx or .doc to .docx, etc. was not to exclude other software from being compatible with MS Office. Rather, it was implemented when MS adapted MS Office to be compatible with and usable with the XML formats that came into being at the time; it was just MS denoting those documents were compatible with use in XML environments. I have taken some, if not all, of other publishers .doc or other file formats and easily open them and used them in MS Office. Likewise, I have had no apparent problems renaming a .docx file to .doc and opening them on other software such as Open Office, etc. The only downside is non-Office software will most often not support some of the formatting features such as XML used by MS, but, since the vast majority of users aren't really using the most "high-end" tech features of Office apps, the effect is virtually nil...
<O>
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