There are really two issues:
(1) The first is your serial number. Full information on finding serial #s is at Find your serial number. Assuming that you purchased your software directly from Adobe (either by phone or website), Adobe Customer Support (accessible eventually via the web page cited above) can help you. If you purchased the software from a third party, you may be out of luck.
(2) The more crushing issue is that Acrobat 7 is only fully compatible with Windows versions no newer than Windows XP 32-bit. At best, if you can coerce Acrobat 7 to install on newer versions of Windows (including Windows Vista, Windows 7, Windows 8.x, and Windows 10), the full product (including the Adobe PDF PostScript printer driver instance used to create PDF by “printing to PDF” as well as the PDFMakers that plug into Microsoft Office for direct PDF generation from those applications) will not properly install and/or work.d
You really are due for a new version of Acrobat. Initially released 11.5 years ago, Acrobat 7 is five versions out-of-date.
- Dov