Just placed a CMYK image into Word 2007, and made a PDF with Acrobat settings set to "Leave Colors Unchanged" and it did indeed make an RGB PDF.
Thanks PrintIT, this is as expected, as MS Office products are sRGB by nature. If you wish to have CMYK or spots from MS products - then one should use MS Publisher.
I have not performed tests to see what MS Office is assuming as the source space of the CMYK file, before it is converted to (s)RGB. Is it using the unknown screen preview colour or is another more complex colour conversion taking place?
I would convert all elements to sRGB before placing them in MS Office, even if MS Office will allow the insertion of CMYK originals. This should allow for closer colour as one can assign/assume the CMYK source profile before going to sRGB.
Setting the Acrobat settings to "convert all colors to CMYK" created a CMYK PDF (but it must be going through conversions twice - CMYK to RGB when bringing it into Word, then RGB to CMYK when making the PDF - sounds like a recipe for color shift).
Ain't Microsoft great?
Forgetting about the image for now, what about the solid black text 0r0g0b? What happens to it when you make a CMYK PDF with your method. My guess is that the final text will be rich black, not 0cmy100k.
Acrobat Pro and the previously mentioned plugs will allow the solid black text 0r0g0b elements to be converted to black only - if the source is RGB to begin with.
I would not blame MS too much in this case, their office software is RGB based and if one is going to try to do CMYK work then one has to know how to deal with input and output to get good results on press. Although one should use the right tool for the job at hand, MS Office files can be taken to press if one knows what they are doing.
EDIT: Attached is a crop of the section of the Acrobat Pro Convert Colours command for converting 0rgb elements to 0cmy100k.
Stephen Marsh