Problems reading text from a file built with InDesign

i downloades the trial version of PDFNet SDK, and i'm testing it.
I have a problem.
I need to develope a pdf file as at this post:
At first i used a file that i found on my file system. And it works
Then i passed a file created with Adobe InDesign. I used InDesign
because i need to build many different pdf schemas with placeholders.
Then i'd like to replace these placeholders using the PDFNet SDK.
In this case the library can't read the text. the
Element::getTextData() method give to me an empty string.
can you give me some help?

You probably want to use GetTextString() instead if
Element::GetTextData(). The latter method returns low-level character
codes which may not have anything to do with Unicode. If this does not
help, could you please include the InDesign file?