This is the structure of QPDFSamplesViewer a sample project using, Android Qoppa’s PDF toolkit, within Android Studio.

Download (containing qoppapdf.jar, libs and assets folder)

Make sure that the libs folder, jniLibs folder and the assets folder are in the correct location so that they are available as resources.

Structure in Android Studio
Note the location of the libs, jniLibs and assets folders.

Make sure to add the jniLibs folder path to the sourceSets in the build.gradle. If your app is not copying the jnilibs folder properly during build process, try to manually recreate the folder.