Reading hyperlinks from pdf file

Question

I\'m trying to read a pdf file and get all hyperlinks from this file. I\'m using iTextSharp for C# .net.

PdfReader reader = new PdfReader(\"test.pdf\");              


        

Answer 1

PdfReader.GetLinks() is only meant to be used with links internal to the document, not external hyperlinks. Why? I don't know.

The code below is based off of code I wrote earlier but I've limited it to links stored in the PDF as a PdfName.URI. Its possible to store the link as Javascript that ultimately does the same thing and there's probably other types but you'll need to detect for that. I don't believe there's anything in the spec that says that a link actually needs to be a URI, its just implied, so the code below returns a string that you can (probably) convert to a URI on your own.

    private static List<string> GetPdfLinks(string file, int page)
    {
        //Open our reader
        PdfReader R = new PdfReader(file);

        //Get the current page
        PdfDictionary PageDictionary = R.GetPageN(page);

        //Get all of the annotations for the current page
        PdfArray Annots = PageDictionary.GetAsArray(PdfName.ANNOTS);

        //Make sure we have something
        if ((Annots == null) || (Annots.Length == 0))
            return null;

        List<string> Ret = new List<string>();

        //Loop through each annotation
        foreach (PdfObject A in Annots.ArrayList)
        {
            //Convert the itext-specific object as a generic PDF object
            PdfDictionary AnnotationDictionary = (PdfDictionary)PdfReader.GetPdfObject(A);

            //Make sure this annotation has a link
            if (!AnnotationDictionary.Get(PdfName.SUBTYPE).Equals(PdfName.LINK))
                continue;

            //Make sure this annotation has an ACTION
            if (AnnotationDictionary.Get(PdfName.A) == null)
                continue;

            //Get the ACTION for the current annotation
            PdfDictionary AnnotationAction = (PdfDictionary)AnnotationDictionary.Get(PdfName.A);

            //Test if it is a URI action (There are tons of other types of actions, some of which might mimic URI, such as JavaScript, but those need to be handled seperately)
            if (AnnotationAction.Get(PdfName.S).Equals(PdfName.URI))
            {
                PdfString Destination = AnnotationAction.GetAsString(PdfName.URI);
                if (Destination != null)
                    Ret.Add(Destination.ToString());
            }
        }

        return Ret;

    }

And call it:

        string myfile = System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "Output.pdf");
        List<string> Links = GetPdfLinks(myfile, 1);

Answer 2

I have noticed that any text on a PDF that looks like a URL can be simulated as a annotation link by the PDF vewer. In Adobe Acrobat there is a page display preference under the general tab called "Create links from URLs" that controls this. I was writing code to remove URL link annotations, only to find that there were none. But yet Acrobat was automatically turning text that looked like a URL into a what appeared to be an annotation link.