is Print options > Print Scaling.
In the File > Print window you should see an option to "Scale to paper size". If that is set, for example, to print an A4 document to an A5 sized sheet, then that may be the cause.
Other than that I am not sure.
Perhaps others here will have different suggestions.
Word 2003 prints most documents at about 2/3 of their size -- both documents I create and documents I receive from others. No other Office program does this. No other non-Office program does this. I can print these files full-size in Open Office Writer.
I reinstalled Word. No help.