After a PDF document has been loaded, document contents and their properties can be read and modified using the properties and methods of TgtPDFDocument object.

In the next code snippet, we first specify the measurement unit that will be used when rendering elements on a PDF page. Next, a HTML-formatted string is written on the last page. The number of the last page is obtained from the property TgtPDFDocument.PageCount().

...

    // Set document measurement units to pixels
    gtPDFDocument1.MeasurementUnit := muPixels;

    // Write formatted text at the center of the last page
    gtPDFDocument1.TextOut(
      '<i>Hello, <b>World!</b></i>',         // HTML-formatted string
      IntToStr(gtPDFDocument1.PageCount),    // Page range
      gtPDFDocument1.                        // X-coordinate
          GetPageSize(gtPDFDocument1.PageCount, muPixels).Width/2,
      gtPDFDocument1.                        // Y-coordinate
          GetPagesize(gtPDFDocument1.PageCount, muPixels).Height/2);

    // Save the modified document
    gtPDFDocument1.SaveToFile('modified_doc.pdf');

...

The formatted string is written at the center of the last page. To obtain the location of the center of the page, we first call TgtPDFDocument.GetPageSize().

function GetPageSize(PageNo: Integer; MMUnit: TgtMeasurementUnit): TgtPageSize;

TgtMeasurementUnit = (muPixels, muPoints, muInches, muMM, muTwips);

TgtPageSize = record
  Width,
  Height: Double;
end;

This method returns a TgtPageSize record, whose fields TgtPageSize.Width and TgtPageSize.Height provide the dimensions of the specified page. From this information, it is easy to calculate the location of the center of the page.

As you can see, PDFtoolkit provides an elegant interface that hides the complexities imposed by the format specification.

The TgtPDFDocument.GetPageElements() is another example of a very capable PDFtoolkit method.

function GetPageElements(
   APageNo: Integer; 
   ElementTypes: TgtElementTypes; 
   MMUnit: TgtMeasurementUnit): TgtPDFPageElementList;

TgtPDFElementType=(etText, etImage, etPath, etFormField);

This method returns a list of PDF page elements from a specified page. If the page element returned by the method is a text element, then its properties expose details such as location, font, and color. If it were an image, then you can get hold of its coordinates, scaling factor, and the actual image in the form of a TGraphic object. That’s the level of control you get with PDFtoolkit.

PDFtoolkit offers more than one way of doing the same thing, each one more useful in a special situation. The TgtPDFDocument.SearchAll() method can perform a variety of text searches for a given search string.

Function SearchAll(
    Const SearchText: String; 
    AOptions: TgtSearchTypes; 
    SearchList: TStringList):Integer;

TgtPDFSearchTypes = (stCaseSensitive, stWholeWord, stNone);

You can also extract all text in one go.

// Returns a list of text extracted from a specified page
function ExtractText(APageNo: Integer): TStringList;
// Returns formatted text extracted from a specified page
function ExtractTextFormatted(APageNo: Integer): TStringList; 

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PDFtoolkit makes merging and splitting files a breeze. Here is a code snippet that shows how to merge several documents into one.

...

var
    gtPDFDocument1: TgtPDFDocument;
    StringList1: TStringList;
begin

  // Create a document object
  gtPDFDocument1 := TgtPDFDocument.Create(Nil);
  // Load a list with names of the
  // documents that need to be merged
  StringList1 := TStringList.Create();
  StringList1.Add('sample_doc1.pdf');
  StringList1.Add('sample_doc2.pdf');
  StringList1.Add('sample_doc3.pdf');

  try
    // Merge the documents
    gtPDFDocument1.MergeDocs(StringList1);
    // Save the merged document to file
    gtPDFDocument1.SaveToFile('merged_doc.pdf');

...

PDFtoolkit can enhance a PDF document in a number of useful ways, such as

• Marking up text
• Hyperlinking images and text
• Adding bookmarks, stamps, and watermarks
• Embedding files as attachments

In this code snippet, we see how to add bookmarks for all pages in a document.

...

var
    I: Integer;
    gtPDFDocument1: TgtPDFDocument;
    // Bookmark 
    gtPDFOutline1: TgtPDFOutline;
    // Destination linked by a bookmark
    gtPDFDestination1: TgtPDFDestination;
    // Display style of a bookmark in bookmark panel
    gtBookmarkAttribute1: TgtBookmarkAttribute;
begin
  gtPDFDocument1 := TgtPDFDocument.Create(Nil);
  try
    gtPDFDocument1.LoadFromFile('sample_doc.pdf');
    if gtPDFDocument1.IsLoaded then
    begin
     // For each page in the document
     for I := 1 to gtPDFDocument1.PageCount do
     begin
      // Create a bookmark that links to the top-left
      // corner of the page in the current iteration
      gtPDFDestination1 :=
         TgtPDFDestination.Create(
           I,      // Number of the page
           dtXYZ,  // Destination type (use x-y coordinates and zoom)
           0,      // X-coordinate of the destination
           0,      // Y-coordinate of the destination
           100);   // Zoom

      // Create bookmarks with maroon-colored, bold-italic text
      gtBookmarkAttribute1 :=
          TgtBookmarkAttribute.Create([fsBold, fsItalic], clMaroon);

      if I = 1 then
      begin
        // If it's the first page, then create a new bookmark
        gtPDFOutline1 := gtPDFDocument1.CreateNewBookmark(
                     'Page #' + IntToStr(I),  // Bookmark title text
                     gtPDFDestination1,
                     gtBookmarkAttribute1);     
      end
      else
      begin
        // For other pages, add a bookmark next to the
        // previously created bookmark
        gtPDFOutline1 := gtPDFOutline1.AddNext(
                    'Page #' + IntToStr(I),  // Bookmark title text
                     gtPDFDestination1,
                     gtBookmarkAttribute1);
      end;
     end;
    end;
    // Save the modified document
    gtPDFDocument1.SaveToFile('modified_doc.pdf');

...

Here is how to encrypt a PDF document.

...
uses
  ...
  gtPDFCrypt,
  gtPDFDoc;

var
    gtPDFDocument1: TgtPDFDocument;
begin

  // Create a document object
  gtPDFDocument1 := TgtPDFDocument.Create(Nil);

  try
    // Load input document
    gtPDFDocument1.LoadFromFile('unencrypted_doc.pdf');

    if gtPDFDocument1.IsLoaded then
    begin
      // Modify documents encryption settings with
      // the TgtPDFEncryption object returned by
      // TgtPDFDocument.Encryption property
      with gtPDFDocument1.Encryption do
      begin
        Enabled := True;
        Level := el128bit;   // 128-bit encryption level
        OwnerPassword := 'Owner';
        UserPassword := 'User';
        UserPermissions
              := [AllowAccessibility,
                  AllowPrint,
                  AllowHighResPrint];
       end;
    end;

    // Save the encrypted document to file
    gtPDFDocument1.SaveToFile('encrypted_doc.pdf');
...

This code snippet shows how to mark page numbers on all pages in a PDF document.

...

var
    I: Integer;
    gtPDFDocument1: TgtPDFDocument;
begin
  gtPDFDocument1 := TgtPDFDocument.Create(Nil);
  try
    gtPDFDocument1.LoadFromFile('sample_doc.pdf');
    
    if gtPDFDocument1.IsLoaded then
    begin
     gtPDFDocument1.MeasurementUnit := muPixels;
     // Write formatted string on all pages
     // at specified location
     gtPDFDocument1.TextOut(
        'Page <%PageNo%> of <%TotPage%>', // page number
        gtPDFDocument1.                   // x-coordinate
        GetPageSize(I, muPixels).Width - 150,
        100);                             // y-coordinate
    end;
    // Save the modified document
    gtPDFDocument1.SaveToFile('numbered_pages_doc.pdf');

...

The text string is written by an overloaded TgtPDFDocument.TextOut() method. The string contains two built-in placeholders for the current page number and the total page number. PDFtoolkit substitutes built-in placeholders with their values at run time.

You can use placeholders with any TgtPDFDocument method that writes text to a document. You can create your own placeholders and have them substituted at run time by writing a handler for the TgtPDFDocument OnCalcVariables() event.

property OnCalcVariables: TgtOnCalcVariablesEvent read FOnCalcVariables write SetOnCalcVariables;

PDFtoolkit can add, edit, fill, and flatten PDF form fields. Editing a PDF form field involves changing its properties such as its looks, position, or interactivity. Filling a PDF form field involves specifying a particular value for the form field and saving the modified form field to the document. Flattening a form field removes all interactivity from the form field but ensures that the form field still looks its original self.

In this code snippet, we see how to add form fields to a document.

...

var
  gtPDFDocument1: TgtPDFDocument;
  // List box form field
  gtPDFFormListBox1: TgtPDFFormListBox;
  // Push button form field
  gtPDFFormPushButton1: TgtPDFFormPushButton;
  // Rectangles
  gtRect1: TgtRect;
  gtRect2: TgtRect;  
begin
  gtPDFDocument1 := TgtPDFDocument.Create(Nil);
  try
    gtPDFDocument1.LoadFromFile('sample_doc.pdf');
    if gtPDFDocument1.IsLoaded then
    begin
      // Set document measurement unit
      gtPDFDocument1.MeasurementUnit := muInches;

      // Specify rectangle position for list box
      gtRect1.Left := 1;
      gtRect1.Right := 2;
      gtRect1.Top := 1;
      gtRect1.Bottom := 2;

      // Create a list box form field
      gtPDFFormListBox1 := TgtPDFFormListBox.Create();
      // Specify name for the list box in the document
      gtPDFFormListBox1.FieldName := 'lstCountry';
      // Add options to the list box
      gtPDFFormListBox1.AddItem('India');
      gtPDFFormListBox1.AddItem('USA');
      gtPDFFormListBox1.AddItem('Russia');
      gtPDFFormListBox1.AddItem('Germany');
      gtPDFFormListBox1.AddItem('Japan');
      gtPDFFormListBox1.AddItem('China');
      // Specify background color for the list box
      gtPDFFormListBox1.BackgroundColor := clWindow;
      gtPDFFormListBox1.BorderColor := clWindowFrame;
      gtPDFFormListBox1.DefaultValue := 'Select a country';

      // Specify location of the list box
      gtPDFFormListBox1.Rect := gtRect1;

      // Add the list box to the last page
      gtPDFDocument1.AddFormField(
         gtPDFFormListBox1,
         gtPDFDocument1.PageCount); // page number

      // Specify rectangle position for submit button
      gtRect2.Left := 1;
      gtRect2.Right := 2;
      gtRect2.Top := 3;
      gtRect2.Bottom := 3.25;

      // Create a push button
      gtPDFFormPushButton1 := TgtPDFFormPushButton.Create();
      gtPDFFormPushButton1.FieldName := 'btnSubmit';
      gtPDFFormPushButton1.NormalCaption := 'Submit';
      gtPDFFormPushButton1.Rect := gtRect2;
      // Set button to submit form contents when
      // it is clicked inside a viewer application
      gtPDFFormPushButton1.Action := pbaSubmit;
      // Specify URL where form contents should be
      // submitted
      gtPDFFormPushButton1.SubmitURL
         := 'http://www.gnostice.com/newsletters' +
            '/demos/200804/forms_test.asp';

      // Add push button to document
      gtPDFDocument1.AddFormField(
        gtPDFFormPushButton1,
        gtPDFDocument1.PageCount);

      // Save the modified document to file
      gtPDFDocument1.SaveToFile('forms_doc.pdf');
    end;

...

PDFtoolkit’s viewer is a visual component that can be used to display PDF documents on a VCL forms application. It does not require Adobe® Reader to be installed on the client machine. The viewer’s API provides methods to implement navigation, zooming, and other toolbar-driven functionality.

...

    gtPDFDocument1: TgtPDFDocument;
    gtPDFViewer1: TgtPDFViewer;
    OpenDialog1: TOpenDialog;
    edFilePath: TEdit;
    edNumberOfPages: TEdit;

...

// Select a PDF document
 if not OpenDialog1.Execute then
  exit;

 // Update text field
 edFilePath.Text := OpenDialog1.FileName;

 // Unload any previously loaded document
 if gtPDFDocument1.IsLoaded then
  gtPDFDocument1.Reset;

 try
   // Load the selected PDF document
   gtPDFDocument1.LoadFromFile(edFilePath.Text);

   // Check if document has been successfully loaded
   if gtPDFDocument1.IsLoaded then
   begin
     // Display number of pages
     edNumberOfPages.Text := IntToStr(gtPDFDocument1.PageCount);
     // Specify document that needs to be
     // displayed by the viewer
     gtPDFViewer1.PDFDocument :=  gtPDFDocument1;
     // Activate viewer
     gtPDFViewer1.Active := True;

...

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PDFtoolkit’s PDF printer is a non-visual component. It has methods and properties that allow a VCL application to query available printers, select a printer, specify print settings, and print a specified set of pages to the selected printer. The most attractive thing about the printer component is that it can print PDF documents without requiring external components such as GhostScript or Adobe® Reader.

PDFtoolkit includes a visual component meant for providing interactive text search capabilities to VCL forms applications. It needs to be used in conjunction with the PDFtoolkit’s viewer component. The functionality of the search panel is similar to the one found in Adobe Reader. See screenshot.

PDFtoolkit has several other components such as the PDFOutlineViewer, which can be used to display a bookmark panel for a PDF document.

In summary, Gnostice PDFtoolkit is a component suite that has well-rounded capabilities in PDF processing.