set image to feature image with function

Hi,
I need to set featured image to posts with function
when I am using below code I can not get the featured images with “$dynamic_featured_image->get_featured_images”

set_post_thumbnail( $post_id, $attachment_id );
add_post_meta($parent_post_id, ‘_thumbnail_id’, $attachment_id);

I find below doc but I can’t find ver. 2.0.2 . for download…

3. Can I set the image from remote url?

If you need to add images from the remote url you need to switch back to ver. 2.0.2 . There is no such feature in ver. 3.0.0 and above.

Note: If you are using remote url to use the feature image, the helper functions may not work properly.
Alt, caption and title attribute for these images cannot be retrieved using helper functions. NULL is returned instead.