Itextsharp open password protected file modify it and adopt protection

Question

I open an existing pdf. Checking for protection and ask for password if it is protected and open it with:

        PdfReader pdfReader = null;
        Stream outputStream = null;
        PdfStamper pdfStamper = null;

        try
        {
            pdfReader = GetPdfReaderObject();
            outputStream = new FileStream(filePathDestination, FileMode.Create, FileAccess.Write, FileShare.None);
            pdfStamper = new PdfStamper(pdfReader, outputStream);

                PdfLayer layer = new PdfLayer("watermark", pdfStamper.Writer);

                for (int pageIndex = 1; pageIndex <= pdfReader.NumberOfPages; pageIndex++) {
                    pdfStamper.FormFlattening = false;
                    iTextSharp.text.Rectangle pageRectangle = pdfReader.GetPageSizeWithRotation(pageIndex);
                    PdfContentByte pdfData = pdfStamper.GetOverContent(pageIndex);

                    pdfData.BeginLayer(layer);

                    PdfGState graphicsState = new PdfGState();
                    graphicsState.FillOpacity = 0.5F;
                    pdfData.SetGState(graphicsState);
                    pdfData.BeginText();

                    iTextSharp.text.Image watermarkImage = iTextSharp.text.Image.GetInstance(System.Drawing.Image.FromFile(watermarkImagePath), ImageFormat.Png);

                    float width = pageRectangle.Width;
                    float height = pageRectangle.Height;

                    watermarkImage.SetAbsolutePosition(width / 2 - watermarkImage.Width / 2, height / 2 - watermarkImage.Height / 2);

                    pdfData.AddImage(watermarkImage);
                    pdfData.EndText();
                    pdfData.EndLayer();
                }
            }
            pdfStamper.Close();
            outputStream.Close();
            outputStream.Dispose();
            pdfReader.Close();
            pdfReader.Dispose();

        } catch (Exception e) {
            ....
        }
    }

After my modifications I save it but the protection is destroyed.

Why the protection is destroyed? How can I save the protection from the origin document und add it to my modified one.

Regards

Please provide more code. You don't show your way of modifying your PDF. Do you use a `PdfStamper`? Or a `PdfCopy`? Or a `PdfWriter`? And how? — mkl, Oct 24 '13 at 12:17

score 3 · Accepted Answer · answered Oct 24 '13 at 13:30

3

You use a PdfStamper to manipulate an existing PDF.

For any source PDF: If you want the result to be encrypted, you may use the SetEncryption method appropriately.

Have a look at the EncryptionPdf.cs, especially its method EncryptPdf:

PdfReader reader = ...;
using (MemoryStream ms = new MemoryStream())
{
    using (PdfStamper stamper = new PdfStamper(reader, ms))
    {
        stamper.SetEncryption(
                USER, OWNER, 
                PdfWriter.ALLOW_PRINTING, 
                PdfWriter.ENCRYPTION_AES_128 | PdfWriter.DO_NOT_ENCRYPT_METADATA
        );
    }
    return ms.ToArray();
}

Here USER and OWNER are the user and owner passwords of your choice. You might want to use a different set of permissions.

For already encrypted source PDFs you may alternatively choose to use the PdfStamper in append mode (i.e. use a PdfStamper constructor with a bool append parameter set to true). In that case the original encryption will also be applied to the updated PDF.

answered Oct 24 '13 at 13:30

mkl

90,588
15
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With the append flag the protection/encryption is also working after modification. But if I opeb the pdf with Acrobat Reader it tells me that: "An error exists on this page. Acrobat may not Display the page correctly. Please contact the Person who created the PDF document to correct the Problem". Do I need to encrypt my new added image also? Are what is the problem? On an document with no encryption it's working without failure. – GermanSniper Oct 25 '13 at 06:30
@GermanSniper Could you provide a sample, both before and after manipulation? – mkl Oct 25 '13 at 10:13
I will provide some sample files later. But one more Problem occours: If I add the tag append I can't remove content from the pdf's. How can I save encryption, delete and add content? Slowly i'm going crazy... – GermanSniper Oct 25 '13 at 11:02
1

An alternative to using append mode is using the *unethical* mode, cf. the discussion under @Bruno's answer. Simply set the static `bool PdfReader.unethicalreading` to `true` and use your `PdfStamper` without append mode. – mkl Oct 25 '13 at 11:49
Here the two sample files with error. I hope u can help me with These. [Sample pdf with error](http://www.file-upload.net/gal-61870/ryg9jw/1.html) – GermanSniper Oct 25 '13 at 16:01
I'll look at them later, i don't have my tools available right now. – mkl Oct 26 '13 at 11:23
@GermanSniper Ok, I looked at your files (BTW, that file service is quite a pain).The manipulated PDF is not encrypted anymore. Which of the proposed methods did you use to create this PDF? `append`? `unethicalreading`? Explicit separate encryption? – mkl Oct 26 '13 at 23:24
oh sry. The files was modified without copy the encryption. Here is an example with encryption. [sample 2 with unethicalreading](http://www.file-upload.net/gal-62249/cyda/1.html) . But always if the source document is encrypted I got an error in my modified pdf document opening with acrobat – GermanSniper Oct 28 '13 at 16:50
Ok I solve the Problem with the pdf invalide Content stream. http://stackoverflow.com/questions/8235339/pdf-generated-with-itext-becomes-corrupted-when-using-setsimplecolumn THX for your help!!!!!! – GermanSniper Oct 30 '13 at 06:57

score 1 · Answer 2 · answered Oct 24 '13 at 13:16

1

Which version of iText are you using?

When a password protected PDF was opened using the owner password and manipulated by PdfStamper, all original password protection was indeed removed. This changed in iText 5.3.5. See the changelog:

Important: we now keep the original owner password when stamping a document.

In other words: with all iText versions prior to 5.3.5, the owner password is lost. Starting with 5.3.5, it should be kept.

answered Oct 24 '13 at 13:16

Bruno Lowagie

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9
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I use version 5.4.3. That can't be the problem – GermanSniper Oct 24 '13 at 13:31
*we now keep the original owner password when stamping a document* - Always? I find a `if (reader.isEncrypted() && (append || PdfReader.unethicalreading)) { crypto = new PdfEncryption(reader.getDecrypt()); }` in the `PdfStamperImp` code which looks like keeping it only in append or unethical mode... – mkl Oct 24 '13 at 13:40
Hmm... I wrote that code. Now that you remind me of unethical mode, I remember: if you know the owner password, you're probably supposed to set the password with `stamper.setEncryption()`. If we automatically reuse the existing password, there's no way to decrypt a document into an unencrypted PDF (which is also a use-case). I gave an up-vote to your answer (and I also up-voted the question as it's a good one). – Bruno Lowagie Oct 24 '13 at 17:14
If i remember Correctly, the check-in comment for adding conditions other than `isEncrypted` was that this made decrypting using the stamper impossible. ;) – mkl Oct 24 '13 at 19:13

Itextsharp open password protected file modify it and adopt protection

2 Answers2