How to check if a PDF is Password Protected or not

Here's a solution that doesn't require 3rd party libraries, using the PdfRenderer API.

 fun checkIfPdfIsPasswordProtected(uri: Uri, contentResolver: ContentResolver): Boolean {
    val parcelFileDescriptor = contentResolver.openFileDescriptor(uri, "r")
        ?: return false
    return try {
        PdfRenderer(parcelFileDescriptor)
        false
    } catch (securityException: SecurityException) {
        true
    }
}

Reference: https://developer.android.com/reference/android/graphics/pdf/PdfRenderer

The way I do it is by attempting to read the PDF file using PdfReader without passing a password of course. If the file is password protected, a BadPasswordException will be thrown. This is using the iText library.

In the old version of PDFBox

try
{
    InputStream fis = new ByteArrayInputStream(pdfBytes);                       
    PDDocument doc = PDDocument.load(fis);

    if(doc.isEncrypted())
    {
      //Then the pdf file is encrypeted.
    }
}

In the newer version of PDFBox (e.g. 2.0.4)

    InputStream fis = new ByteArrayInputStream(pdfBytes);
    boolean encrypted = false;
    try {
        PDDocument doc = PDDocument.load(fis);
        if(doc.isEncrypted())
            encrypted=true;
        doc.close();
    }
    catch(InvalidPasswordException e) {
        encrypted = true;
    }
    return encrypted;

Use Apache PDFBox - Java PDF Library from here:
Sample Code:

try
{
    document = PDDocument.load( "C:\\abc.pdf");

    if(document.isEncrypted())
    {
      //Then the pdf file is encrypeted.
    }
}