Android differences between signed and unsigned .apk files?

Question

How many difference between signed and unsigned .apk files in android?

I know only one when i integrate in-app purchase i have unsigned .apk its gives me error

Answer 1

If you send unsigned apk to customer, they have to enable Unknown sources to be able to install the app. Also Google Play Console doesn't accept unsigned one.

Answer 2

the signed apk will contain an extra folder "META-INF", which contains three files:

1. MANIFEST.MF
2. CERT.SF
3. CERT.RSA