Finding text in PDF

Q: Our PDFs contain invisible text as part of the PDF, we would like to find the position of these texts (basically marker ids) and put a colored square just above the text which the user should be able to click.

Could you point us to some APIs/code fragments to implement such a feature?
A: If the invisible text is searchable, then we would recommend either TextSearch (see example here) or TextExtract (see example here). Then you can get the coordinates of the text and use this coordinate to perform tasks you wish to achieve (i.e. adding a new annotation or adding a view on top of the control etc.).