Is it possible to determine whether an array of bytes represents a pdf file that cannot be edited?

Question

Context

I have two steps in my service, uploading and downloading the file. When uploading to the service I receive the data through an array of ASCII bytes.

This data is stored in a database. In the download, the data referring to the file is fetched from the database and written in binary to a temporary file.

From there, I place a watermark, and return the download of the final file to the user. It is a PDF file.

The Problem

The problem is that when the user uploads a file (PDF) it cannot be edited. This is not a read-only attribute, because the data is being searched in the database, and not in the user’s computer.

What characterizes the "editability" the file is an assigned permission within the PDF format when the file is protégé.

Goal

What I try to understand is if there is a way to identify if the file:

1. It’s a protected PDF
2. If the editing permission has been assigned by the file creator

So I can handle the application flow and prevent a non-enterable file from being stored in the database (and eventually an error is thrown in by not being able to add the watermark.).

Exemplo do byte[]:

    [0] 37  

    [1] 80  

    [2] 68  

    [...] ... 

    [84006] 10  

Remembering that, currently, my solution is to write the file in a temporary location inside the server to make this check. I want to avoid this step and perform any verification directly in the data array I receive from the database.

To rebuild the file from the data stored in the database, I use the following resource:

BinaryWriter Writer = new BinaryWriter(System.IO.File.OpenWrite(fileName));
Writer.Write("variavel_byte[]");

Answer 1

There is a solution without using the Byte Array using iTextSharp, with byte array found nothing, including in other searches all point to the components.

PM> Install-Package iTextSharp

---

    using iTextSharp.text.pdf;

    private void CheckPdfProtection()
    {
        var filePath = @"c:\temp\EmploymentHistory.pdf";
        using (var reader = new PdfReader(filePath))
        {
            if (!reader.IsEncrypted()) return;

            if (!PdfEncryptor.IsPrintingAllowed(Convert.ToInt32(reader.Permissions)))
                throw new InvalidOperationException("Arquivo protegido para impressão");
            if (!PdfEncryptor.IsModifyContentsAllowed(Convert.ToInt32(reader.Permissions)))
                throw new InvalidOperationException("Arquivo protegido para escrita");
        }
    }