The user documentation for extensions released before ArcGIS 9.1 is available in PDF format on the CD entitled 'ESRI Software Documentation Library' in the ArcGIS Desktop 9.1 Media Kit. However, user documentation is not available in PDF format for the extensions that were released with ArcGIS 9.1, Network Analyst and Schematics. Documentation for these extensions is available from the ArcGIS Desktop Online Help.
This documentation can be accessed by navigating to Help > ArcGIS Desktop Help from either ArcCatalog or ArcMap, or by visiting the ESRI Online Support Center, available at the link provided in the Related Information section below.
If the ArcTutor data has been installed, the ArcTutor exercises for these extensions are available at the following location: <ArcGIS_Installation_location>\ArcTutor\Tutorial_Docs