If your organization never purchased PowerBuilder 10.5, you cannot legally download or use it. In this case, consider:
This specific version introduced several significant enhancements to the PowerBuilder ecosystem: DataWindow Innovations: powerbuilder 10.5 download
Offered native interfaces for major databases and expanded support for Web Services: If your organization never purchased PowerBuilder 10
If your company originally purchased PowerBuilder 10.5 licenses (either standalone or as part of an SAP/Sybase suite), you are legally entitled to access the installer. the demand remains real.
Despite its age, the demand remains real.