How to find which app opens a file type on Android
You tap a PDF and it opens in an app you don't remember choosing. You want to change it, so you go to Settings… and there's nothing there. Android has Default apps for your browser, phone and SMS app, but no screen that lists which app opens each file type.
Why Android makes this hard
- File-type defaults aren't stored by file type. When you tap Always in the “Open with” dialog, Android saves that preference on the app, not on the file type. So to find the default for PDFs, you have to look inside each app.
- The settings only say “some defaults set”. An app's page tells you it has defaults, but not which file types they're for.
- Phone makers rename everything. It's Open by default on Pixel, Set as default on Samsung, and something else again on other phones.
- Defaults disappear silently. Installing another app that can open the same type often clears your choice, so the “Open with” dialog comes back without explanation.
Method 1: open a file and watch what happens
- Open a file of that type, for example a PDF from your Downloads.
- If an Open with dialog appears, there is no default for that type yet.
- If it opens straight into an app, that app is the default.
This tells you which app, but not how to change it. For that, see Method 2.
Method 2: check each app's settings
- Open Settings → Apps and choose the app you think is the default.
- Tap Open by default (Pixel) or Set as default (Samsung).
- If it says No defaults set, it isn't the default for anything. If you see Clear default preferences (or Clear defaults) and it can be tapped, the app is the default for at least one file type or action.
The catch: Android won't tell you which types. If you have a dozen file viewers, you're checking a dozen apps.
See every file-type default at once
Defaultify for Android lists 100+ file types, from PDF and DOCX to MKV, ZIP and code files, with the app that opens each one and every other app that could. The Apps Overview shows the reverse: which file types each app has claimed.
Changing the default once you've found it
- In the app's Open by default / Set as default page, tap Clear default preferences.
- Open the file again. The Open with dialog appears.
- Pick the app you want and tap Always.
Clearing defaults clears all of that app's file-type choices, not just one, so you may need to re-pick a few.