How do I extract attachments from a pdf file?

Question

I have a big number pdf documents with xml files attached to them. I would like to extract those attached xml files and read them. How can I do this programatically using .net?

Answer 1

iTextSharp is also quite capable of extracting attachments... Though you might have to use the low level objects to do so.

There are two ways to embed files in a PDF:

1. In a File Annotation
2. At the document level "EmbeddedFiles".

Once you have a file specification dictionary from either source, the file itself will be a stream within the dictionary labeled "EF" (embedded file).

So to list all the files at the document level, one would write code (in Java) as such:

Map<String, byte[]> files = new HashMap<String,byte[]>();

PdfReader reader = new PdfReader(pdfPath);
PdfDictionary root = reader.getCatalog();
PdfDictionary names = root.getAsDict(PdfName.NAMES); // may be null
PdfDictionary embeddedFilesDict = names.getAsDict(PdfName.EMBEDDEDFILES); //may be null
PdfArray embeddedFiles = embeddedFilesDict.getAsArray(PdfName.NAMES); // may be null

int len = embeddedFiles.size();
for (int i = 0; i < len; i += 2) {
  PdfString name = embeddedFiles.getAsString(i); // should always be present
  PdfDictionary fileSpec = embeddedFiles.getAsDict(i+1); // ditto

  PdfDictionary streams = fileSpec.getAsDict(PdfName.EF);
  PRStream stream = null;

  if (streams.contains(PdfName.UF))
    stream = (PRStream)streams.getAsStream(PdfName.UF);
  else
    stream = (PRStream)streams.getAsStream(PdfName.F); // Default stream for backwards compatibility

  if (stream != null) {
    files.put( name.toUnicodeString(), PdfReader.getStreamBytes((PRStream)stream));
  }
}