In order to view remote documents from an HTTP URL, cleartext network traffic support is required. On Android 9.0 (API level 28) or higher, cleartext support is disabled by default and apps targeting Android 9.0 or higher will need to add the android:usesClearTextTraffic="true" flag in the AndroidManifest.xml file.

Example:

<?xml version="1.0" encoding="utf-8"?>
<manifest ...>

    <!-- Required permissions are added here -->
    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.RECORD_AUDIO" />

    <!-- Add multidex support and enable largeHeap -->
    <application 
        android:name="android.support.multidex.MultiDexApplication"
        android:largeHeap="true"
+       android:usesCleartextTraffic="true"
        ...>    
        ...
    </application>
</manifest>