I have searched and searched but none of the suggested fixes works. I have Acrobat 8 Professional and have hundreds of A4 drawing files saved as PDFs in landscape mode but no matter what I try they always open in portrait. This has probably been posted dozens of times before but my searches reveal nothing.
Here's a link to the help section on rotate.
http://help.adobe.com/en_US/Acrobat/8.0/Professional/help.php?content=WS3E35FEEB-6B69-41aa-BC78-A0AF1977CC26.php