What is an APK File?

Every app on the Google Play Store is delivered as an APK (or a newer format called AAB that gets converted to an APK on Google's servers before delivery). As of 2024, the Google Play Store hosts over 3 million apps — every single one distributed and installed as an APK (Statista, 2024). When you tap "Install" in the Play Store, Android is silently downloading and installing an APK in the background. When you install an app manually — outside the Play Store — you are doing the same thing, just more directly. That process is called sideloading.

What is Inside an APK File?

An APK is actually a ZIP archive. If you rename an .apk file to .zip and open it, you will find a structured set of directories and files:

• AndroidManifest.xml — the app's ID (package name), declared permissions, minimum Android version, and entry points. This is the first thing Android reads when you install an APK.
• classes.dex — the compiled app code in Dalvik Executable format. This is the bytecode that Android's runtime (ART) executes.
• res/ — images, layouts, strings, and other resource files used by the UI.
• assets/ — raw files the app ships with, such as fonts, audio, or bundled databases.
• lib/ — compiled native libraries (.so files) for different CPU architectures (ARM, x86, etc.).
• META-INF/ — the APK's digital signature and certificate. Android uses this to verify the APK has not been tampered with and to associate updates with the correct developer.
• resources.arsc — a compiled resource table that maps resource IDs to the actual strings and values.

Knowing this structure matters because it explains why you cannot run an APK directly on Windows — the .dex code is meant for Android's ART runtime, not a PC processor. You need an actual Android device (or an Android emulator) to run it.

How APKs Are Created

Developers write Android apps in Kotlin or Java using Android Studio. When they build a release version of their app, the build tools compile the source code into .dex bytecode, package everything together, compress it, and sign it with the developer's private key. The resulting file is an APK.

The signature is important. When you install an update to an app, Android checks that the new APK is signed with the same key as the installed version. If the signatures do not match, Android refuses the update. This is a security feature that prevents anyone from shipping a fake update to replace a legitimate app.

Why Would You Install an APK Manually?

The Google Play Store covers the vast majority of use cases, but there are real reasons to install APKs directly:

Apps not available on the Play Store

Some apps are only distributed through their developer's website — enterprise apps, apps for specific hardware, or apps that did not pass Google's review. F-Droid, an open-source app repository, also distributes only APKs since it is entirely independent of Google.

Region-locked apps

Many apps are only available on the Play Store in certain countries. If you travel or live in a region where an app is not listed, downloading the APK from a trusted mirror like APKMirror is a common workaround.

Beta versions

Developers sometimes share pre-release APKs with testers directly — via email, Discord, or their own website — before a version is on the Play Store. QA testers and app reviewers deal with this constantly.

Older versions

If a Play Store update broke something you relied on, you can roll back by installing an older APK. APKMirror maintains version archives for many popular apps.

Modified or forked apps

Open-source apps sometimes have community forks with extra features. These will never appear on the Play Store but are distributed as APKs through GitHub releases or similar channels.

How to Enable Installing APKs From Outside the Play Store

Android blocks installations from unknown sources by default. Here is how to allow them:

Android 8.0 and later (per-app permission)

1. Go to Settings and search for Install unknown apps.
2. Tap the app you want to use as the installer (a file manager, a browser, or Andora on the PC side).
3. Toggle Allow from this source on.

This permission is granted per installer app, which is more secure than a global toggle because it limits which apps can initiate installs.

Android 7.x and earlier (global toggle)

1. Go to Settings > Security.
2. Enable Unknown sources.

How to Install an APK From a PC

Installing an APK from your PC is much faster and more reliable than transferring the file to the device and tapping through the installer UI. There are two approaches:

Using ADB on the command line

With ADB installed and USB debugging enabled, run:

adb install path\to\yourapp.apk

Android handles the rest. There is no "Unknown Sources" prompt because ADB installs bypass the usual on-device installer flow.

Using Andora (no terminal needed)

Andora lets you drag and drop an APK onto its window and click Install. No terminal, no ADB setup, no PATH configuration. See the full step-by-step in our tutorial: how to install APK from PC.

Security Considerations

APK files carry the same risks as any executable file on any platform. Here is how to stay safe:

• Download from the developer's official website whenever possible. If an app has a GitHub releases page, use that.
• Use APKMirror for popular apps — they verify every APK signature against the original Play Store version before hosting it.
• Avoid random APK hosting sites that exist solely to serve APK downloads. Many repackage legitimate apps with added malware.
• Check permissions in the manifest — if a simple flashlight app requests access to your contacts and location in its APK manifest, that is a red flag.
• Use Google Play Protect — even for sideloaded apps, Play Protect can scan installed packages and flag suspicious ones.

For a deeper look at the sideloading process itself — risks, trusted sources, and best practices — read our guide on what APK sideloading is.