t$ = pdf.GetBoundedText(id, page, left, top, right, bottom)
left, top, right, and bottom from a page. If there is no text within the specified
bounding rectangle, an empty string is returned.
The page to use must be specified in the page argument. It must be a number in
the range of 1 to the total number of pages in the document and the page must have
been previously loaded using pdf.LoadPage() with the text argument set
to True. The PDF document specified by id must have been previously opened using
pdf.OpenDocument().