Window redraw event.
[event] redraw([in] LONG dc, [in] int left, [in] int top, [in] int right, [in] int bottom)
This event will be called whenever the XpdfViewer window (or a portion of the window) needs to be redrawn. This can be used to draw arbitrary content on top of the PDF file.

The arguments provide a DC and the region that is being redrawn.

Private Sub viewer_redraw(dc As Long, left As Long, top As Long, _ right As Long, bottom As Long) _ Handles viewer.redraw ' use Windows GDI functions here... End Sub