Unfortunately, you have no control over how your users open your document,
but you can make the following suggestions in your cover email:

1. Recipients may be grateful for information on how to disable Reading
Layout view (Tools | Options | General).

2. As I understand it, a document won't open in Reading Layout view unless
it is opened directly from an attachment; this is a bad idea for many
reasons, so you might encourage your recipients to first save the document
to their hard drive. It will then open in the view in which you have saved
it.

Failing that, the only thing that would force Print Layout view would be a
macro; if users have Macro Security set to High or Very High, the macro
would be tacitly disabled; if they have security set to Medium, they might
still choose to disable it.