This is what products and service like ADEPT (http://www.adobe.com/products/adept/) are for. However, the entry price might be a little steep. Essentially, the answer is no, you can't prevent people from copying the PDF - it's just a normal file after all. All you can do is prevent people who aren't allowed to open the file. This is what the encryption is for (in part). But the trick is to somehow provide each valid user with the appropriate key to open the book. This can be done one by one in Acrobat with the password feature. Or one can use ACS (Adobe's DRM system) but that has been discontinued. Or, one can use ADEPT.