Pick and display a pdf file

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:text="PICK FILE"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:text="0/0"
        android:textSize="20dp"
        app:layout_constraintStart_toEndOf="@id/button1"
        app:layout_constraintBottom_toTopOf="@id/imageView"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintEnd_toStartOf="@id/button2"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="80dp"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:text="PREV"
        app:layout_constraintEnd_toStartOf="@+id/button3"
        app:layout_constraintStart_toEndOf="@+id/textView1"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button3"
        android:layout_width="80dp"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:text="NEXT"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:scaleType="fitCenter"
        android:background="@color/white"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button2"
        android:layout_margin="8dp"
        android:elevation="8dp"
        tools:srcCompat="@tools:sample/backgrounds/scenic" />

</androidx.constraintlayout.widget.ConstraintLayout>

package com.example.pickfile;

import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.pdf.PdfRenderer;
import android.net.Uri;
import android.os.Bundle;
import android.os.ParcelFileDescriptor;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import java.io.FileNotFoundException;
import java.io.IOException;

public class MainActivity extends AppCompatActivity {

    TextView textview1;
    ImageView imageview1;

    PdfRenderer renderer;
    int total_pages = 0;
    int display_page = 0;
    public static final int PICK_FILE = 99;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button button1 = findViewById(R.id.button1);
        Button button2 = findViewById(R.id.button2);
        Button button3 = findViewById(R.id.button3);
        textview1 = findViewById(R.id.textView1);
        imageview1 = findViewById(R.id.imageView);

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
                intent.addCategory(Intent.CATEGORY_OPENABLE);
                intent.setType("application/pdf");
                startActivityForResult(intent, PICK_FILE);
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // move to previous page
                if (display_page > 0) {
                    display_page--;
                    _display(display_page);
                }
            }
        });

        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // move to next page
                if (display_page < (total_pages - 1)) {
                    display_page++;
                    _display(display_page);
                }
            }
        });

    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == PICK_FILE && resultCode == RESULT_OK){
            if (data != null){
                Uri uri = data.getData();
                try {
                    ParcelFileDescriptor parcelFileDescriptor = getContentResolver()
                            .openFileDescriptor(uri, "r");
                    renderer = new PdfRenderer(parcelFileDescriptor);
                    total_pages = renderer.getPageCount();
                    display_page = 0;
                    _display(display_page);
                } catch (FileNotFoundException fnfe){

                } catch (IOException e){

                }
            }
        }
    }

    private void _display(int _n) {
        if (renderer != null) {
            PdfRenderer.Page page = renderer.openPage(_n);
            Bitmap mBitmap = Bitmap.createBitmap(page.getWidth(), page.getHeight(), Bitmap.Config.ARGB_8888);
            page.render(mBitmap, null, null, PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY);
            imageview1.setImageBitmap(mBitmap);
            page.close();
            textview1.setText((_n + 1) + "/" + total_pages);
        }
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        if (renderer != null){
            renderer.close();
        }
    }

}