Thank you for your post! Avenza Maps is only compatible with Android OS 5.0 and newer. If you are able to update your Android OS to version 5.0 or newer, you will be able to download Avenza Maps from the Google Play Store. You can check to see if your device can update by going to your device Settings > About.
If you have any further questions please let me know!
We do not recommend downloading APKs from the internet. If you download the APK from the internet we cannot be held liable if there are any issues, and we do not support any versions prior to Avenza Maps 3.3 because we do not support Android OS 4.4.
If you decide to download the APK from the internet, the version that you need is Avenza Maps 3.2.