I have an old, licit version of Acrobat 5 that I just decided to install on my G5, as a downgrade from X.5 to X.4 and thus to Classic potentiality has been in the making.

The installer required booting Classic, which was expected. It transpires, however, that in order to run the program, Classic is not required, despite the stated system requirements. It runs in Tiger.

I quote from the readme:

• System Requirements
   
  System Requirements for Acrobat and Acrobat Distiller for Macintosh
   
  -PowerPC® processor
  -Apple® Mac® OS 8.6, 9.0.4, or 9.1
  -32 MB of RAM (with virtual memory on) (64 MB recommended)
  -120 MB of available hard-disk space for an Easy Installation of Acrobat 5.0
  -Additional 32 MB of hard-disk space for Asian fonts (optional)
  -CD-ROM drive
   
  The installer creates temporary files during installation so the actual hard disk space required during installation is greater than the values listed above.
   
  System Requirements for Acrobat Reader Macintosh
   
  -PowerPC® processor
  -Apple® Mac® OS 8.6, 9.0.4, or 9.1
  -16 MB of RAM (24 recommended)
  -24 MB of available hard disk space
  -Additional 32 MB of hard-disk space for Asian fonts (optional)
   
  Web Browser Support
   
  The web browsers within which PDF files may be viewed, using either Acrobat or Acrobat Reader, are:
  Internet Explorer 5.0
  Netscape Navigator 4.x
  

That's rather old software, running fine in X.4.11 (and no, Classic definitely has not started up). Is there an explanation for this unexpected boon?