How to use php to force a File Download box to pop up

When I work today, I need to force a Download box to be filled out after the user visits a page. I remember seeing the code snippet of this function on a forum. the result was not found, that's depressing. Later, Google came to a website and made a few decisions. at the same time, I would like to share with you the need to force a Download box after the user visits a page, I remember seeing the code snippet of this function on a forum. it was easy to find and the result was not found. it was depressing. Later, Google came to the game and made a few decisions. at the same time, I would like to share with you. The code is as follows:
$ Filename = "1.bmp"; // Image address, which can be an absolute or relative address
Header ("Content-Type: application/force-download ");
Header ('content-Disposition: attachment; filename = "'. $ filename .'"');
$ Img = file_get_contents ($ filename );
Echo $ img;
?>
This function is actually very practical. for example, in order to prevent other people from leeching resources, we should first provide a encrypted connection and users cannot download it after clicking it outside the site. Such a function needs to be implemented by the above code.