Tracking Application Install Referral With APK

I have an application using which anyone can share the apk of the app itself. The APK will be generated using PackageManager class like this:

File file = new File(packageManager.getApplicationInfo(packagename, PackageManager.GET_META_DATA).publicSourceDir)

I need to track (deep link or some other way), who installs the app and who sent the referral? At first, it seemed infeasible to me. Then I came to know that chinese apps like Helo and WeLike actually do so. I gave it a try. When we share the application from inside of it (have no idea how they generate APK, but the method is probably the same since I have checked they are not getting the APK from remote server and APK size is 40 MB and App Size is 40 MB so they mustn't be storing the APK in the package itself), the person who installs that APK is given the referral prize and relevant information like who referred is shown. How is this possible? I would like to know any possible way.

In short, how can I track APK installs just with an APK file and no link (but includes generating APK from app ofcourse).

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