Fix 701286: Check and ask for file permissions in DocumentActivity.
diff --git a/lib/build.gradle b/lib/build.gradle
index fcddbf2..1dba8f2 100644
--- a/lib/build.gradle
+++ b/lib/build.gradle
@@ -5,6 +5,7 @@
 version = '1.16.1'
 
 dependencies {
+	implementation 'androidx.appcompat:appcompat:1.1.+'
 	if (file('../jni/build.gradle').isFile())
 		api project(':jni')
 	else
diff --git a/lib/src/main/java/com/artifex/mupdf/viewer/DocumentActivity.java b/lib/src/main/java/com/artifex/mupdf/viewer/DocumentActivity.java
index 2cfc936..d3e0ce0 100644
--- a/lib/src/main/java/com/artifex/mupdf/viewer/DocumentActivity.java
+++ b/lib/src/main/java/com/artifex/mupdf/viewer/DocumentActivity.java
@@ -1,5 +1,6 @@
 package com.artifex.mupdf.viewer;
 
+import android.Manifest;
 import android.app.Activity;
 import android.app.AlertDialog;
 import android.content.Context;
@@ -7,6 +8,7 @@
 import android.content.DialogInterface;
 import android.content.Intent;
 import android.content.SharedPreferences;
+import android.content.pm.PackageManager;
 import android.content.res.Resources;
 import android.database.Cursor;
 import android.graphics.Color;
@@ -39,6 +41,9 @@
 import android.widget.TextView;
 import android.widget.ViewAnimator;
 
+import androidx.core.app.ActivityCompat;
+import androidx.core.content.ContextCompat;
+
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
@@ -51,6 +56,7 @@
 	enum TopBarMode {Main, Search, More};
 
 	private final int    OUTLINE_REQUEST=0;
+	private final int    PERMISSION_REQUEST=0;
 	private MuPDFCore    core;
 	private String       mFileName;
 	private ReaderView   mDocView;
@@ -154,6 +160,8 @@
 				Uri uri = intent.getData();
 				System.out.println("URI to open is: " + uri);
 				if (uri.getScheme().equals("file")) {
+					if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_DENIED)
+						ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, PERMISSION_REQUEST);
 					String path = uri.getPath();
 					core = openFile(path);
 				} else {