You can view a pdf file in an android project in different ways. I will describe some of them here-

1. Using Library: Steps are below:

Installation Add to build.gradle: implementation 'com.github.barteksc:android-pdf-viewer:2.8.2'
ProGuard If you are using ProGuard, add following rule to proguard config file:
-keep class com.shockwave.**
Include PDFView in your layout
<com.github.barteksc.pdfviewer.PDFView android:id="@+id/pdfView" android:layout_width="match_parent" android:layout_height="match_parent"/>
Further link is here
2. Load pdf url into webview:

webview = (WebView)findViewById(R.id.webview);
    progressbar = (ProgressBar) findViewById(R.id.progressbar);
    webview.getSettings().setJavaScriptEnabled(true);
    String filename = file_url_with_name;
    webview.loadUrl(file_url + filename);

    webview.setWebViewClient(new WebViewClient() {

        public void onPageFinished(WebView view, String url) {
            // do your stuff here
            progressbar.setVisibility(View.GONE);
        }
    });

3. Manually show PDF file into Imageview

// Example for creating manual PDF viewer into imageview used butterknife view binding<br/>

public class PdfRenderActivity extends AppCompatActivity {

    @BindView(R.id.pdf_image) ImageView imageViewPdf;
    @BindView(R.id.button_pre_doc) FloatingActionButton prePageButton;
    @BindView(R.id.button_next_doc) FloatingActionButton nextPageButton;

    private static final String FILENAME = "report.pdf";

    private int pageIndex;
    private PdfRenderer pdfRenderer;
    private PdfRenderer.Page currentPage;
    private ParcelFileDescriptor parcelFileDescriptor;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_pdf_render);
        ButterKnife.bind(this);
        pageIndex = 0;
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    @Override
    protected void onStart() {
        super.onStart();
        try {
            openRenderer(getApplicationContext());
            showPage(pageIndex);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    @Override
    public void onStop() {
        try {
            closeRenderer();
        } catch (IOException e) {
            e.printStackTrace();
        }
        super.onStop();
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    @OnClick(R.id.button_pre_doc)
    public void onPreviousDocClick(){
        showPage(currentPage.getIndex() - 1);
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    @OnClick(R.id.button_next_doc)
    public void onNextDocClick(){
        showPage(currentPage.getIndex() + 1);
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    private void openRenderer(Context context) throws IOException {
        // In this sample, we read a PDF from the assets directory.
        File file = new File(context.getCacheDir(), FILENAME);
        if (!file.exists()) {
            // Since PdfRenderer cannot handle the compressed asset file directly, we copy it into
            // the cache directory.
            InputStream asset = context.getAssets().open(FILENAME);
            FileOutputStream output = new FileOutputStream(file);
            final byte[] buffer = new byte[1024];
            int size;
            while ((size = asset.read(buffer)) != -1) {
                output.write(buffer, 0, size);
            }
            asset.close();
            output.close();
        }
        parcelFileDescriptor = ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);
        // This is the PdfRenderer we use to render the PDF.
        if (parcelFileDescriptor != null) {
            pdfRenderer = new PdfRenderer(parcelFileDescriptor);
        }
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    private void closeRenderer() throws IOException {
        if (null != currentPage) {
            currentPage.close();
        }
        pdfRenderer.close();
        parcelFileDescriptor.close();
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    private void showPage(int index) {
        if (pdfRenderer.getPageCount() <= index) {
            return;
        }
        // Make sure to close the current page before opening another one.
        if (null != currentPage) {
            currentPage.close();
        }
        // Use `openPage` to open a specific page in PDF.
        currentPage = pdfRenderer.openPage(index);
        // Important: the destination bitmap must be ARGB (not RGB).
        Bitmap bitmap = Bitmap.createBitmap(currentPage.getWidth(), currentPage.getHeight(),
                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.
        currentPage.render(bitmap, null, null, PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY);
        // We are ready to show the Bitmap to user.
        imageViewPdf.setImageBitmap(bitmap);
        updateUi();
    }

    /**
     * Updates the state of 2 control buttons in response to the current page index.
     */
    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    private void updateUi() {
        int index = currentPage.getIndex();
        int pageCount = pdfRenderer.getPageCount();
        prePageButton.setEnabled(0 != index);
        nextPageButton.setEnabled(index + 1 < pageCount);
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    public int getPageCount() {
        return pdfRenderer.getPageCount();
    }

}

Doc is here

I'd recommend considering MuPDF which has already been ported for use on Android several times without reliance on Java. MuPDF is optimized for lightweight on-screen PDF rendering, making it perfect for mobile use.

Please note that MuPDF and all the derived projects are not suitable for the commercial use and you should consider alternatives if you are not developing an open source GPL project.

Use below code for that.

First.java

public class First extends ListActivity {

    String[] pdflist;
    File[] imagelist;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.main);

        File images = Environment.getExternalStorageDirectory();
        imagelist = images.listFiles(new FilenameFilter() {
            public boolean accept(File dir, String name) {
                return ((name.endsWith(".pdf")));
            }
        });
        pdflist = new String[imagelist.length];
        for (int i = 0; i < imagelist.length; i++) {
            pdflist[i] = imagelist[i].getName();
        }
        this.setListAdapter(new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, pdflist));
    }

    protected void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);
        String path = imagelist[(int) id].getAbsolutePath();
        openPdfIntent(path);
    }

    private void openPdfIntent(String path) {
        try {
            final Intent intent = new Intent(First.this, Second.class);
            intent.putExtra(PdfViewerActivity.EXTRA_PDFFILENAME, path);
            startActivity(intent);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Second.java

public class Second extends PdfViewerActivity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
    }

    public int getPreviousPageImageResource() {
        return R.drawable.left_arrow;
    }

    public int getNextPageImageResource() {
        return R.drawable.right_arrow;
    }

    public int getZoomInImageResource() {
        return R.drawable.zoom_in;
    }

    public int getZoomOutImageResource() {
        return R.drawable.zoom_out;
    }

    public int getPdfPasswordLayoutResource() {
        return R.layout.pdf_file_password;
    }

    public int getPdfPageNumberResource() {
        return R.layout.dialog_pagenumber;
    }

    public int getPdfPasswordEditField() {
        return R.id.etPassword;
    }

    public int getPdfPasswordOkButton() {
        return R.id.btOK;
    }

    public int getPdfPasswordExitButton() {
        return R.id.btExit;
    }

    public int getPdfPageNumberEditField() {
        return R.id.pagenum_edit;
    }
}

And declared both activities into your manifest file.