The default page view of a PDF document can be set in Acrobat. This has nothing to do with Photoshop. This is metadata-based information that PS doesn't generate.
Editing a PDF in Photoshop will rasterise it. This may be fine, but also may cause extreme damage. Text will no longer be searchable, interactivity and accessibility are lost. For many people, editing PDF in Photoshop is a catastrophe.