Source: Markus Krüger (NOA developer)

The following code shows how to replace OpenOffice.org placeholders added via 'Insert -> Field -> Others... -> Functions -> Placeholder (Text)':

  ...
  ITextDocument textDocument = ...;
  ITextFieldService textFieldService = textDocument.getTextFieldService();
  ITextField[] placeholders = textFieldService.getPlaceholderFields();
  for (int i = 0; i < placeholders.length; i++) {
    String placeholderDisplayText = placeholders[i].getDisplayText();
    placeholders[i].getTextRange().setText("Text for " + placeholderDisplayText);
  }

It is important to know, that the array of placeholders is not in any order, so you have to use the method "getDisplayText()" to check if it is the correct placeholder you want to replace.