Depending on the format of the file, this can vary substantially between trivial and impossible. Do you have any information about the format specification? Is it a binary or ASCII (text file)? If you open the file in a text editor (Notepad or similar), is the text meaningful? Without some more information about the file format, we will be unable to help you further.
I did a quick Google search for *.03D files and couldn't find anything.
