pdfSetRegionLabel
Update a highlighted region's label.
void pdfSetRegionLabel(PDFViewerHandle viewer, PDFRegionHandle region, char *label)
This function changes the label for the specified highlighted region.
The region handle comes from pdfAddRegion, pdfGetRegion, or
pdfGetSelectedRegion.
C:
pdfSetRegionLabel(viewer, region, "new label");