There is a detailed answer from Rahul on StackOverflow about this that I wanted to highlight by blogging about it.
There is also one thing to add to it.
The Design Automation engines do not support having dlls and other resources for multiple versions in the same app bundle - you cannot rely on the PackageContents.xml file to specify which files should be used by which engine version.
If you need to use different dlls and other resources for different engine versions, then you should create a separate app bundle (or app bundle version) for each engine version that you want to support, and a separate activity (or activity version) that is referencing the correct app bundle version - as discussed in the StackOverflow answer.
Follow @AdamTheNagy Adam Nagy joined Autodesk back in 2005 and has been providing programming support, consulting, training and evangelism to external developers. He started his career in Budapest, then worked in Prague for 3 years and now lives in South England, UK. At the moment focusing on Inventor and Fusion 360, plus cloud and mobile related technologies. Adam has a degree in Software Engineering and has...