Delete page option missing in Adobe Acrobat

This is a recent development - the delete option is missing from multi-page PDFs that I create.  I think the issue is in the security settings, but I can't figure out how to turn on the delete option, or change the security options in my document.  I've started using Drawboard PDF to delete pages - I'm able to delete pages in there.
Any thoughts on why there is no delete option?  
How can I fix this?