Open Packaging Format is the predecessor of the popular EPUB format. It is not that well supported in modern programs or devices and rarely used nowadays. However you can still produce these files with some ebook management programs, you would be better off with EPUB format though.
Convert Microsoft Word document (prior version 2007) to Open Packaging Format.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert doc to opf on Windows
Free Creator for Mobipocket eBooks
Convert from doc file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.