status = doc:SetOpenAction(dst)
doc:SetOpenAction() set the first page to appear when a document is opened. dst must be a valid destination
object created by page:CreateDestination().
When doc:SetOpenAction() succeeds, it returns #HPDF_OK. Otherwise, it returns an error code and the error handler is called.
#HPDF_INVALID_DOCUMENT - An invalid document handle was set.
#HPDF_FAILED_TO_ALLOC_MEM - Memory allocation failed.
#HPDF_INVALID_DESTINATION - An invalid destination object was set.