Auto switch from default Two Pages (if used by the user) to Single Page page layout if a document has only 1 page would be a sensible feature to have.
Foxit pdf software does this be default. If a user uses Two Pages page layout and opens a document containing only 1 page, page layout is automatically switched to Single Page page layout and all other page layout options (Single page continuous, Two page, Two page continuous) are greyed out (disabled) as there is only 1 page in the document.
Document has 2 or more pages (Two Page page layout is used if a user has selected it in preferences as the default page layout option and all other page layout options are available)

Document has only 1 page (Single Page page layout is automatically activated and all other page layout options are greyed out):

Thank you.