Word 2008 doesn't convert the file format of any file it can open. The
'conversion' message you may be seeing would be less misleading if the word
"interpreting" were used instead. Because of internal changes to how the
2008 version works it needs to make the interpretation in order to display
the file content ‹ especially graphics created in the older versions. The
file format (.doc), however, isn't affected in any way.
The only times a 'Convert File' dialog appears is if the file is in
something other than .doc/.docx (such as .rtf) *and* the Word preference is
set for 'Confirm conversion on open' -or- if Word can't recognize the format
of the file you're attempting to open. If you're regularly seeing this
dialog it's probably because of how the file was saved & how it was handled
by email transmittal that's causing it to be triggered.
Likewise, when you save the changes the .doc file is updated accordingly
based on that format. One exception is if you're actually using the Save As
command rather than Save. If that's the case, you're telling Word to create
a new copy of the file & it will default to saving in it's native .docx
format. That can be modified in either of two ways.
One option is to simply choose the Word 97-2004 Document (.doc) format from
the list of Formats in the Save As dialog. The other option would be to go
into Word> Preferences> Save to select that format as the default for new
documents. If you do the latter, however, you'll need to change to the .docx
format for any other files you create. I'd be reluctant to do so because the
new format is significantly better for many reasons.
Another consideration is if you use the features of 2008 which aren't
supported by the .doc format, such as SmartArt, Document Elements & certain
others designed for the OXML format. If you have to preserve the older file
format it's probably best to avoid the use of the newer features in those
documents. But there's another factor to consider as well...
If the users you're exchanging files with are using PC Word 2000 or later or
Mac Word v.X or later & have kept their software updated they do have the
ability to open files saved in the OXML (.docx) format. Free filters are
available from Microsoft for exactly that purpose. Once the package is
installed Word 2003/2004 can do so directly from the File Menu whereas the
older versions must have the files passed through the conversion app first.
If you're experiencing something different please explain in step-by-step
detail exactly how you are proceeding, what the wording is of any messages
that are displaying, at what points in the process those messages appear, as
well as any other details you can supply.