pdfSetRotate
Change the page rotation.
void pdfSetRotate(PDFViewerHandle viewer, int rotate)
This function changes the current rotation angle. The angle is in
degrees and can be 0 (the default), 90, 180, or 270. Normally, a PDF
file specifies the correct rotation for each page (e.g., 90 degrees
for landscape pages) - XpdfViewer handles this automatically, and the
rotate property isn't needed. The rotate property is primarily useful
with misconfigured PDF files that don't have the correct page rotation
set.
C:
pdfSetRotate(viewer, 90);