So, you're right that license for a developer to distribute the PB run time is free. However, I'm afraid the rest isn't as easy as you may be thinking.
First problem is that not only do you have to match the run time versions down to the minor version level (e.g. 10.5), but down to the build level (e.g. 10.5.2.7826). Another complicating factor discerning the build level is that the properties that I believe you're looking at can be manipulated prior to the build of the executables, so those attributes may or may not reflect reality.
The second problem is distribution. The intention was/is that developers distribute their own run times, so they can include the correct DLLs necessary for the functionality implemented, the correct version, etc.... There isn't a mechanism for end users (AFAIK) to go somewhere and say: I have an app from 10.5.2.7826 that uses DataWindows, rich text, XML and web services; please give me the corresponding DLLs. The intended mechanism is that the DLLs come from the development environment where the application was built.
Even if you were to go to the lengths of getting your hands on a PB 10.5 environment, and correctly knew which version to patch to, there's additional problems getting patches (not insurmountable, but a PITA worth noting). Due to both this version (10.5) no longer being supported, and to a conflict with the former third party provider for the ODBC drivers for PB 10.5, the patches aren't freely downloadable. You have to contact Sybase tech support to get these patches.
Bottom line: The way this should be done is to get the run time DLLs from the developer. Failing that, I'm not aware of any other route (legal, official) that getting a copy of PowerBuilder, patching it and harvesting the DLLs yourself.
The cynical bottom line: The developer that didn't bundle the DLLs with the executable: epic fail. <grin
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Good luck,
Terry.