Hi

Thanks for looking at the fix and confirming it (mostly) works. I am though interested in what the additional fix was that you had to add and if (and how) it differs from the pdf spec

I recently encountered a file that gave me this error as well. I did some digging and now have a good idea behind the bug.

Specifically it occurs with encryption algorithm 4, security handler revision 4 and encrypt metadata set to true.

The error is in the function CalculateEncryptionKey in StandardEncrypt.cs

For reference in the pdf spec from Adobe for 1.7 (https://www.adobe.com/content/dam/acom/en/devnet/pdf/PDF32000_2008.pdf) in section 7.6.3.3 in Algorithm 2 (page 61 and 62) point F says

(Security handlers of revision 4 or greater) If document metadata is not being encrypted, pass 4 bytes with the value of 0xFFFFFFFF to the MD5 hash function

Below is the original section of code.

if (revision >= 4 && encryptMetadata)
            {
                byte[] b = new byte[4];
                for (int i = 0; i < 4; ++i)
                {
                    b[i] = 0xFF;
                }

                tmp.AddRange(bytes);
            }

First of all in the IF statement it is meant to be if NOT encrypted

Second of all, the wrong variable is being added to tmp. The variable containing the value 0xFFFFFFFF is named "b" not "bytes"

The variable "bytes" has previously been declared as the bytes of the permissions for the pdf

Below is the fixed section

if (revision >= 4 && !encryptMetadata)
            {
                byte[] b = new byte[4];
                for (int i = 0; i < 4; ++i)
                {
                    b[i] = 0xFF;
                }

                tmp.AddRange(b);
            }

After that the pdf I had worked fine

Our experience for this was with an edit-restricted PDF file. The file opens in Adobe Acrobat but page extraction, document changing, etc are restricted. These restrictions are facilitated by encrypting the PDF.

On attempting to import the PDF with PdfFormatProvider this message is encountered.
System.InvalidOperationException: Password is not correct.