Can't send file in proper format

Hello,
I have had some trouble with uploading a file that I’ve created into email or another site and sending it, and it seems to be formatted incorrectly. The recipient can’t open/read it.
I always choose to format it in some version of MSWord, but they all have an x in the end of the description, i.e. docx. I think this is new.

I’ve just installed the new libreofice 4.0.0.3, and now I can’t open any of my own files.

Help, please?
(I’m not very techie, so please walk me through whatever steps you may have).
Many thanks!

The ‘.docx’ extension appears when you save your LibreOffice document as a MS Word 2007/2010 document:

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…and only versions 2007 or later of MS Word can open it directly. It is also possible to open such documents with MS Word 2003 after installing a compatibility module available free from Microsoft.

But it is easier to save it directly as a MS Word 2003 document from the “File → Save as…” menu:

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