As I understand your post you need to be concerned about copyright protection that prevents others from using your work as their own.
That gets into legal matters and I (full disclosure) am not an attorney or other legal entity.
And there is very little that you can do to prevent cut and paste copying per se. And cut and paste for research and reference purposes is probably allowable via the fair use clauses and other related legal guidelines.
Now you can protect the file itself via a password protected folder and/or encryption that would prevent people from copying the file itself if that is your requirement. And you can password protect the individual .pdf file to prevent it from being opened.
Sort of depends on the details and the degree to which you wish to "add difficulties".