Accessing PDF annotations

Some PDF documents contain annotations, bits of data that are associated with specific regions of a PDF document's pages.

All annotations share a base set of possible attributes; functions for accessing these base attributes are established by the com.snowtide.pdf.annot.Annotation interface. These attributes include an annotation's name (typically unique within the page on which the annotation is found), text contents (also used as a description field when the annotation's primary content is non-text, as in a file attachment), and the region on the document's page where the annotation is placed.

PDFxStream provides richer implementations for four types of annotations:

PDF annotation type	PDFxStream type
Text notes ("stickies")	com.snowtide.pdf.annot.TextAnnotation
Styled text attachments	com.snowtide.pdf.annot.FreeTextAnnotation
Links (referring to a position within the PDF document or to local or network resources)	com.snowtide.pdf.annot.LinkAnnotation
File attachments	com.snowtide.pdf.annot.FileAttachmentAnnotation

The additional attributes provided by these classes are well documented in the linked API reference pages.

Actually accessing PDF annotations is accomplished using either com.snowtide.pdf.Document.getAllAnnotations() (to get a list of all annotations, document-wide) or com.snowtide.pdf.Document.getAnnotations(int) (to get a list of all annotations on a given page).

Here is a code sample where all of the link annotations are retrieved from a PDF document, and their URI's are printed to standard out:

import com.snowtide.PDF;
import com.snowtide.pdf.Document;
import com.snowtide.pdf.annot.*;

public class ExtractLinks {
    public static void main (String[] args) throws java.io.IOException {
        String pdfFilePath = args[0];

        try (Document doc = PDF.open(pdfFilePath)) {
            for (Annotation a : doc.getAllAnnotations()) {
                if (a instanceof LinkAnnotation) {
                    LinkAnnotation link = (LinkAnnotation)a;
                    if (link.getURI() != null) {
                        System.out.printf(
                          "Found outgoing link on page %s, bounds %s, uri: %s",
                          link.pageNumber(), link.bounds(), link.getURI());
                        System.out.println();
                    }
                }
            }
        }
    }
}

Note that LinkAnnotation instances may also refer to a position within the PDF document using a page number and precise bounding coordinates as some bookmarks do; this data can be used to drive a selective text extraction process.