Before you go any further, please read my page on "No Copies - No Editing."
https://www.addbalance.com/word/nocopies.htm#StartPage
The ultimate answer is that although you can make things harder, you cannot stop copying, though. In the final analysis, though, this goes back to the aphorism that if two people know a secret, it is no longer a secret.
If you protect a document / restrict editing for "filling in forms," text cannot be selected for copying. It is not difficult to overcome this protection, nor the "No Changes" protection Filip suggested. The "filling in forms" is highly intrusive protection and you may want "No changes" instead, with the addition of a shape.
If you follow Filip's suggestion, I'm afraid text can still be selected and copied into the clipboard. However, you could, before applying the restriction, add a borderless rectangle with transparent fill in front of your text. Anyone trying to copy would select the rectangle, not the text. That has to be done for each page of the document.