Accessing PDF annotations
Some PDF documents contain annotations, bits of data that are associated with specific regions of a PDF document’s pages. Annotations include:
- Text notes ("stickies")
- Styled text attachments
- Links (referring to a position within the PDF document or to local or network resources)
- File, audio, and video attachments
- Drawings and in-line graphics
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:
- text notes (
com.snowtide.pdf.annot.TextAnnotation
) - styled text attachments (
com.snowtide.pdf.annot.FreeTextAnnotation
) - links (
com.snowtide.pdf.annot.LinkAnnotation
) - attachments (
com.snowtide.pdf.annot.FileAttachmentAnnotation
)
The additional attributes provided by these functions are well documented in the linked API reference pages; 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]; 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(); } } } doc.close(); } }
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.