It is certainly possible to convert Android APK files to BAR format, so Android apps can be used on Blackberry Playbook, unfortunately the opposite aka bar to apk conversion is not possible. Which means that there is no way how to transfer BlackBerry apps saved as .bar files to .apk files for Android platform, mainly due the fact that Android OS lacks the BB unique runtime.
You can find utilities such as the BAR to APK Converter, but users report that it is not reliable enough and may not work for most .bar files. Most developers of BB apps also provide a version for Android, so you can check the app's developer website for more clues.Open BAR file Open APK file
A bar to apk conversion tool