Discard diagonal text when doing text extraction.
void pdfSetDiscardDiagonalText(PDFViewerHandle viewer, BOOL discard)
During text extraction, all text on a page is assigned to one of four rotations (0, 90, 180, or 270 degrees). Normally, text is assigned to the closest rotation value.

If this function is called with discard true, any text that's not close to one of the 0, 90, 180, or 270 degree axes, is discarded. This is useful to skip watermarks drawn on top of body text, etc.

pdfSetDiscardDiagonalText(viewer, TRUE);