Home » Newsletter » October 2006

Making Select Keywords Active with Link Annotations in PDF

Want to make instances of a particular text or keyword linked to a destination elsewhere in the document? Read on!

By Ramya H. N.

PDFtoolkit allows you to find occurrences of a word or phrase in any page of a PDF document with its search routines SearchFirst and SearchNext.

A link annotation could be inserted in these occurrences to a destination somewhere else in the document using the InsertAnnotation method with any of the following actions:

A go-to action that changes the current view to a specified destination.
A remote go-to action that jumps to a destination in another PDF file.
A launch action that launches an application file or opens/prints a document file.
A URI action that causes a uniform resource identifier (URI) to be resolved (usually opened in a browser).

By adding a link annotation to the occurrence of a particular word or phrase using PDFtoolkit, you can make that word or phrase an active link in the PDF file that users can interact with.

Here are the steps to add link annotations to all occurences of a given search text in a PDF file:

Load the input file: A call to the Loadfromfile() method loads the input file into the gtPDFDocument component.
```
 ...
 gtPDFDocument.Loadfromfile('Input.pdf');
 ...
```
Search for all instances of a text in the input file: The method SearchAll() returns the number of the instances of a given text in the input PDF file. This method populates the objects array of string list SearchResult with all PDF text elements containing the search text. With these text elements, you can identify the locations where the link annotation needs to be inserted.
```
 ...
 SearchResult := TStringList.Create;
 Count := gtPDFDocument.SearchAll(
                                  Text,
                                  [stWholeWord],
                                  SearchResult
                                 );
 ...
```

Insert the link annotation for each identified instance of the search text: To highlight the location of the link annotations, you can use TgtPDFLineAnnotation. Create instances of TgtPDFLineAnnotation and TgtPDFLinkAnnotation, and set their properties.

Next, insert link and line annotations at each instance of the search text in the PDF document - a call made to InsertAnnotation() with the link annotation object and PageNumber as arguments.

 ...
 LineAnnot := TgtPDFLineAnnotation.Create;
 LineAnnot.LineBeginingStyle := laNone;
 LineAnnot.LineEndingStyle := laNone;
 LinkAnnot := TgtPDFLinkAnnotation.Create;
 URI := TgtPDFURIAction.Create ;
 URI.URI := edLink.Text;
 LinkAnnot.Action := URI;
 for LI := 0 to Count - 1 do
 begin
   LinkAnnot.RectLeft := TgtPDFTextElement(SearchResult.
     Objects[LI]).XCordOrigin;
   LinkAnnot.RectTop := TgtPDFTextElement(
     SearchResult.Objects[LI]).YCordOrigin;
   LinkAnnot.RectRight := LinkAnnot.RectLeft
     + PDFDoc.GetCharWidth(Trim('Text'),
     TgtPDFTextElement(SearchResult.Objects[LI]).Font);
    LinkAnnot.RectBottom := LinkAnnot.RectTop -
      TgtPDFTextElement(SearchResult.Objects[LI]).
      Font.Height;
    LineAnnot.gtLine(LinkAnnot.RectLeft,
      LinkAnnot.RectBottom + 2, LinkAnnot.RectRight,
      LinkAnnot.RectBottom + 2);
    gtPDFDocument.InsertAnnotation(
      LinkAnnot, TgtPDFTextElement(
      SearchResult.Objects[LI]).PageNumber);
    gtPDFDocument.InsertAnnotation(LineAnnot,
      TgtPDFTextElement(SearchResult.Objects[LI]).
      PageNumber);
  end;
 ...

Save the enhanced output file and display: The output file is saved when a call is made to the SaveToFile() method.
```
 ...
 gtPDFDocument.SaveToFile('Output.pdf');
 ...
```

This PDF file contains link annotation with URI action. When the mouse pointer moves over the search text ("Pascal"), the link annotation will be displayed. Clicking the annotation opens the link in a browser.

---o0O0o---

Downloads:

Plain text file containing module source code for this project. Here, we search the occurrence of text represented by two variables Text1 and Text2 in the document. Link annotations are added with URI actions for Text1 and remote go-to actions for Text2 respectively.

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