New Install of Word2007 freezing when opening large Word2003 doc

I transferred a Word 2003 MS Word .doc from an external hard drive to my new
computer with 2007 newly installed.

At times, the program freezes before completion of the 187-page document
loading.

Other times, the document completely loads but freezes when I click into the
document and try to type.

The MS Word program has run an automatic detection program and found one
issue, which is says was successfully corrected (it did not tell me the
issue).

I have noticed that my .doc has been automatically saved as a .docx. Could
this be the issue?

Any advice and help would be greatly appreciated. I need to access this
document (and my former computer with 2003 is no longer available to me -
besides, I'd like to use this new computer with the upgraded program).

Thank you.
LB