How to detect if a Word document is password protected before uploading the file to server?

Question

I am working on a website, which allows users to upload different file formats. We need to restrict the user from uploading password protected files.

Is there a way

Answer 1

Give this code a try:

public static Boolean IsProtected(String file)
{
    Byte[] bytes = File.ReadAllBytes(file);

    String prefix = Encoding.Default.GetString(bytes.Take(2).ToArray());

    // Zip and not password protected.
    if (prefix == "PK")
        return false;

    // Office format.
    if (prefix == "ÐÏ")
    {
        // XLS 2003
        if (bytes.Skip(0x208).Take(1).ToArray()[0] == 0xFE)
            return true;

        // XLS 2005
        if (bytes.Skip(0x214).Take(1).ToArray()[0] == 0x2F)
            return true;

        // DOC 2005
        if (bytes.Skip(0x20B).Take(1).ToArray()[0] == 0x13)
            return true;

        // Guessing
        if (bytes.Length < 2000)
            return false;

        // DOC/XLS 2007+
        String start = Encoding.Default.GetString(bytes.Take(2000).ToArray()).Replace("\0", " ");

        if (start.Contains("E n c r y p t e d P a c k a g e"))
            return true;

        return false;
    }

    // Unknown format.
    return false;
}