pdfUri = "file:///storage/emulated/0/myFolder/test.pdf"
Intent pdfViewerIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(pdfUri));
pdfViewerIntent.setType("application/pdf");
PackageManager packageManager = context.getPackageManager();
List<ResolveInfo> activities = packageManager.queryIntentActivities(pdfViewerIntent, 0);

if (activities.size() > 0) {
    context.startActivity(pdfViewerIntent);
} else {
    Toast.makeText(context, "No PDF Viewers installed.", Toast.LENGTH_LONG).show();
}