The activation servers were discontinued by Adobe a number of years ago and Adobe no longer provides a “workaround” version with serial number that doesn't require activation.
Furthermore, even if you could get around the activation issue, Acrobat 7 cannot be installed and be fully functional on any version of Windows beyond 32-bit Windows XP or any 64-bit version of Windows. This includes using later versions of Windows in XP compatibility mode. Why? Very simple. The Adobe PDF PostScript printer driver instance used for PDF creation from Windows application via distillation of PostScript had to be changed in order to be compatible with versions of Windows beyond XP (beginning with Vista) and 64-bit versions of Windows due to (a) changes in the Windows print/spooling system effective with Vista and (b) requirements of 64-bit Windows for 64-bit components that were not available in Acrobat 7. Thus, per Test_Screen_Name 's response, you need to move to the current version of Acrobat.