您可以通过导入使用一个简单的方法

implementation 'com.github.barteksc:android-pdf-viewer:2.8.2'

XML代码为

<com.github.barteksc.pdfviewer.PDFView
        android:id="@+id/pdfv"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </com.github.barteksc.pdfviewer.PDFView>

只需声明并添加一个文件到资产文件夹并分配名称

   PDFView  pdfView=findViewById(R.id.pdfv);       
    pdfView.fromAsset("agl.pdf").load();

以下是如何在不使用任何第三方库的情况下从PDF文件中获得位图缩略图的方法。

private fun loadThumbnailFromPdfFile(file:File, thumbnailImageView: ImageView) {
        Log.d(TAG, "loadThumbnailFromPdfFile: ")
        val mFileDescriptor = ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY)
        // This is the PdfRenderer we use to render the PDF.
        val mPdfRenderer = PdfRenderer(mFileDescriptor)
        //check if pdf have no pages then we can't show pdf thumbnail
        if (mPdfRenderer.pageCount <= 0) {
            //No pages in pdf, can't show thumbnail
            Log.d(TAG, "loadThumbnailFromPdfFile: No pages in pdf")
        } else {
            //There are page(s) in pdf, can show pdf thumbnail
            //Use `openPage` to open a specific page in PDF.
            val mCurrentPage = mPdfRenderer.openPage(0)
            // Important: the destination bitmap must be ARGB (not RGB).
            val bitmap = Bitmap.createBitmap(mCurrentPage.width, mCurrentPage.height, Bitmap.Config.ARGB_8888)
            // Here, we render the page onto the Bitmap.
            // To render a portion of the page, use the second and third parameter. Pass nulls to get
            // the default result.
            // Pass either RENDER_MODE_FOR_DISPLAY or RENDER_MODE_FOR_PRINT for the last parameter.
            mCurrentPage.render(bitmap, null, null, PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY)
            // We are ready to show the Bitmap to user.
            thumbnailImageView.setImageBitmap(bitmap)
        }
    }

因为API Level 21 (Lollipop) Android提供了一个PdfRenderer类:

// create a new renderer
 PdfRenderer renderer = new PdfRenderer(getSeekableFileDescriptor());

 // let us just render all pages
 final int pageCount = renderer.getPageCount();
 for (int i = 0; i < pageCount; i++) {
     Page page = renderer.openPage(i);

     // say we render for showing on the screen
     page.render(mBitmap, null, null, Page.RENDER_MODE_FOR_DISPLAY);

     // do stuff with the bitmap

     // close the page
     page.close();
 }

 // close the renderer
 renderer.close();

有关更多信息，请参阅示例应用程序。

对于旧的api，我推荐Android PdfViewer库，它非常快速和容易使用，在Apache许可证2.0下授权:

pdfView.fromAsset(String)
  .pages(0, 2, 1, 3, 3, 3) // all pages are displayed by default
  .enableSwipe(true)
  .swipeHorizontal(false)
  .enableDoubletap(true)
  .defaultPage(0)
  .onDraw(onDrawListener)
  .onLoad(onLoadCompleteListener)
  .onPageChange(onPageChangeListener)
  .onPageScroll(onPageScrollListener)
  .onError(onErrorListener)
  .enableAnnotationRendering(false)
  .password(null)
  .scrollHandle(null)
  .load();

我有GoogleDrive选项的问题，有时它会无法加载文档和“com.github.barteksc:android-pdf-viewer:2.7.0”，虽然它的文档使它看起来很容易从链接加载文档，但我未能使它工作。它总是抛出一个FileNotFoundException异常，因此经过进一步研究，我了解到它下载pdf，因此您必须使它指向该文档，我发现这有点乏味。

你可以试试这个库。它非常容易使用，并且至今仍在维护，我不知道几年之后他们是否会停止更新它。它会缓存文档，你甚至不需要跟踪它的路径。

https://levelup.gitconnected.com/open-pdf-files-in-android-without-webviews-or-intents-3cc960752cca

public class MyPdfViewActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    WebView mWebView=new WebView(MyPdfViewActivity.this);
    mWebView.getSettings().setJavaScriptEnabled(true);
    mWebView.getSettings().setPluginsEnabled(true);
    mWebView.loadUrl("https://docs.google.com/gview?embedded=true&url="+LinkTo);
    setContentView(mWebView);
  }
}

我从这篇文章和其他类似文章的一些答案中得出了一个混合的方法:

此解决方案检查PDF阅读器应用程序是否已安装，并执行以下操作: —如果设备上安装了PDF阅读器，请将PDF文件下载到设备上，并打开PDF阅读器应用 —如果没有安装阅读器，请询问用户是否希望通过谷歌Drive在线查看PDF文件

注意!这个解决方案使用了在API9 (Android 2.3或Gingerbread)中引入的Android DownloadManager类。这意味着它不能在Android 2.2或更早的版本上运行。

我在这里写了一篇关于它的博客文章，但为了完整性，我在下面提供了完整的代码:

public class PDFTools {
    private static final String GOOGLE_DRIVE_PDF_READER_PREFIX = "http://drive.google.com/viewer?url=";
    private static final String PDF_MIME_TYPE = "application/pdf";
    private static final String HTML_MIME_TYPE = "text/html";

    /**
     * If a PDF reader is installed, download the PDF file and open it in a reader. 
     * Otherwise ask the user if he/she wants to view it in the Google Drive online PDF reader.<br />
     * <br />
     * <b>BEWARE:</b> This method
     * @param context
     * @param pdfUrl
     * @return
     */
    public static void showPDFUrl( final Context context, final String pdfUrl ) {
        if ( isPDFSupported( context ) ) {
            downloadAndOpenPDF(context, pdfUrl);
        } else {
            askToOpenPDFThroughGoogleDrive( context, pdfUrl );
        }
    }

    /**
     * Downloads a PDF with the Android DownloadManager and opens it with an installed PDF reader app.
     * @param context
     * @param pdfUrl
     */
    @TargetApi(Build.VERSION_CODES.GINGERBREAD)
    public static void downloadAndOpenPDF(final Context context, final String pdfUrl) {
        // Get filename
        final String filename = pdfUrl.substring( pdfUrl.lastIndexOf( "/" ) + 1 );
        // The place where the downloaded PDF file will be put
        final File tempFile = new File( context.getExternalFilesDir( Environment.DIRECTORY_DOWNLOADS ), filename );
        if ( tempFile.exists() ) {
            // If we have downloaded the file before, just go ahead and show it.
            openPDF( context, Uri.fromFile( tempFile ) );
            return;
        }

        // Show progress dialog while downloading
        final ProgressDialog progress = ProgressDialog.show( context, context.getString( R.string.pdf_show_local_progress_title ), context.getString( R.string.pdf_show_local_progress_content ), true );

        // Create the download request
        DownloadManager.Request r = new DownloadManager.Request( Uri.parse( pdfUrl ) );
        r.setDestinationInExternalFilesDir( context, Environment.DIRECTORY_DOWNLOADS, filename );
        final DownloadManager dm = (DownloadManager) context.getSystemService( Context.DOWNLOAD_SERVICE );
        BroadcastReceiver onComplete = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                if ( !progress.isShowing() ) {
                    return;
                }
                context.unregisterReceiver( this );

                progress.dismiss();
                long downloadId = intent.getLongExtra( DownloadManager.EXTRA_DOWNLOAD_ID, -1 );
                Cursor c = dm.query( new DownloadManager.Query().setFilterById( downloadId ) );

                if ( c.moveToFirst() ) {
                    int status = c.getInt( c.getColumnIndex( DownloadManager.COLUMN_STATUS ) );
                    if ( status == DownloadManager.STATUS_SUCCESSFUL ) {
                        openPDF( context, Uri.fromFile( tempFile ) );
                    }
                }
                c.close();
            }
        };
        context.registerReceiver( onComplete, new IntentFilter( DownloadManager.ACTION_DOWNLOAD_COMPLETE ) );

        // Enqueue the request
        dm.enqueue( r );
    }

    /**
     * Show a dialog asking the user if he wants to open the PDF through Google Drive
     * @param context
     * @param pdfUrl
     */
    public static void askToOpenPDFThroughGoogleDrive( final Context context, final String pdfUrl ) {
        new AlertDialog.Builder( context )
            .setTitle( R.string.pdf_show_online_dialog_title )
            .setMessage( R.string.pdf_show_online_dialog_question )
            .setNegativeButton( R.string.pdf_show_online_dialog_button_no, null )
            .setPositiveButton( R.string.pdf_show_online_dialog_button_yes, new OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    openPDFThroughGoogleDrive(context, pdfUrl); 
                }
            })
            .show();
    }

    /**
     * Launches a browser to view the PDF through Google Drive
     * @param context
     * @param pdfUrl
     */
    public static void openPDFThroughGoogleDrive(final Context context, final String pdfUrl) {
        Intent i = new Intent( Intent.ACTION_VIEW );
        i.setDataAndType(Uri.parse(GOOGLE_DRIVE_PDF_READER_PREFIX + pdfUrl ), HTML_MIME_TYPE );
        context.startActivity( i );
    }
    /**
     * Open a local PDF file with an installed reader
     * @param context
     * @param localUri
     */
    public static final void openPDF(Context context, Uri localUri ) {
        Intent i = new Intent( Intent.ACTION_VIEW );
        i.setDataAndType( localUri, PDF_MIME_TYPE );
        context.startActivity( i );
    }
    /**
     * Checks if any apps are installed that supports reading of PDF files.
     * @param context
     * @return
     */
    public static boolean isPDFSupported( Context context ) {
        Intent i = new Intent( Intent.ACTION_VIEW );
        final File tempFile = new File( context.getExternalFilesDir( Environment.DIRECTORY_DOWNLOADS ), "test.pdf" );
        i.setDataAndType( Uri.fromFile( tempFile ), PDF_MIME_TYPE );
        return context.getPackageManager().queryIntentActivities( i, PackageManager.MATCH_DEFAULT_ONLY ).size() > 0;
    }

}