Get/set the page rotation.
[read/write property] rotate([out, retval] int *rotate) rotate([in] int rotate)
This property contains 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 it's not necessary to change the rotate property. The rotate property is primarily useful with misconfigured PDF files that don't have the correct page rotation set.
viewer.rotate = 90