Tried hard, contacted Adobe support and did a lot of research:
The PDF will open with the page layout set in Preferences unless a different page layout is selected in Document Properties (File > Properties > Open View). The setting in Document Properties overrides the setting in Preferences. If you use Document Properties, be sure to save and close the document to apply the changes. Acrobat users can change the view on open unless changes have been prevented by security settings. Reader users cannot change the view when opening.
This is not absolutely user-unfriendly and hard to catch and I don't know how to save a PDF in 75% or 50% size, so that PDF is always opened in a fixed size. Thanks!