Hi, If I post some download links within wordpress post , can I hide these links till the visitor make a comment on the same post or at least register first then the links appear ? thanks
For the former, you'd have to use JavaScript, which of course is easily bypasable. You'd be better off using a PHP conditional to feed the download link to your registered users.
There might be, but I'm not sure. I haven't seen any, since this will require connecting to the database.