Digitally sign a PDF on iOS / Android

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Sep 26, 2012, 8:01:31 PM9/26/12
  Can I digitally sign a PDF with "PDFNet Mobile PDF SDK " on iOS / Android ?
Yes, the current version of PDFNet Mobile SDK currently support digital signatures. To obtain a demo version please fill out with detailed information related to your app.
The following sample code shows how to use the new API to digitally sign PDF:
JAVA        :
Ojective C :
C/C++       :
Python      :
C#             :


Sep 26, 2012, 8:03:21 PM9/26/12
Note: some of the above links are incorrect. Correct links to samples are:


Oct 4, 2012, 8:50:53 PM10/4/12
Q: Can you describe what the APIs for PDF digital signatures, with what backends it works with, what is the technology and how the user uses it,  Or perhaps you have a paper describing this feature?
To briefly describe PDFNet's digital signatures API, it is essentially a framework for signing PDF documents. The API is designed to be flexible to allow as much fine grain control for users. The most important component of this API is PDFNet's SignatureHandler interface. The implementation of SignatureHandler is what will provide PDFNet the code and logic to cryptographically sign a PDF file. The SignatureHandler interface provides the following methods for the user to implement:

1. GetName - Gets the name of the SignatureHandler. The name of the SignatureHandler is what identifies this SignatureHandler from all others. This name is also added to the PDF as the value of /Filter entry in the signature dictionary.

2. AppendData - Adds data to be signed. This data will be the raw serialized byte buffer as the PDF is being saved to any stream.

3. Reset - Resets any data appending and signature calculations done so far. This method should allow PDFNet to restart the whole signature calculation process.

4. CreateSignature - Calculates the actual signature using client implemented signing methods. The returned value (byte array) will be written as the /Contents entry in the signature dictionary.

The general usage of PDFNet's digital signatures API will be as follows:

1. Implement the SignatureHandler interface. The implementation details are left up to the user. The sample code that we provide uses OpenSSL to create digital signatures using PKCS#7 standards (the recommended standard for signing PDF files), but the user is free to use any other cryptographic libraries like Botan, Crypto++, Common Crypto (for OSX), CryptoAPI (for Windows), and so on.

2. Open the PDF file to sign with PDFDoc class. Register the implemented SignatureHandler to this PDFDoc instance.

3. Create or select an existing signature form field from the PDFDoc and assign the implemented SignatureHandler to this form field.

4. Save the PDFDoc. During this stage, PDFNet will check for any signature form fields that are associated with SignatureHandler. If there are such associations, PDFNet will perform the necessary steps (by calling implemented code in SignatureHandler) to add signature to the form field.

There can be more intermediary processing between steps 3 and 4 (like adding digital signature appearance). For more details, please see the sample code below.
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