A PDF document can be forced to display in landscape mode each time the document is executed by configuring a setting in the document editor in Design View. Note that if the Landscape option is selected while in .pdf view (i.e., after the document has been executed), the document will only be available in landscape mode for that execution.
Therefore, to set the document to display in Landscape each time it is executed, select the Page Setup option in Design View from the File Menu in the upper-left corner, as shown below:
Check the 'Landscape' radio button under Orientation in the Page Setup window and click 'OK', as shown below:
Save the document prior to executing. By doing so, the document will always be displayed in Adobe Reader in Landscape mode.
