Add programmatically a downloadable file to Woocommerce products [duplicate]

Answer 1

Update 2 (Added an if statement to allow download generation to only one file)

The following code will auto add a downloadable file made from the product image (The download title comes from the EXIF data title).

You should better use dedicated woocommerce_admin_process_product_object action hook and available CRUD objects and getters / setters methods introduced with woocommerce 3 this way:

add_action( 'woocommerce_admin_process_product_object', 'auto_add_downloadable_file', 50, 1 );
function auto_add_downloadable_file( $product ){
    // Get downloads (if there is any)
    $downloads = (array) $product->get_downloads(); 

    // Only added once (avoiding repetitions
    if( sizeof($downloads) == 0 ){
        // Get post thumbnail data
        $thumb_id = get_post_thumbnail_id( $product->get_id() );
        $src_img  = wp_get_attachment_image_src( $thumb_id, 'full');
        $img_meta = wp_get_attachment_metadata( $thumb_id, false );

        // Prepare download data
        $file_title = $img_meta['image_meta']['title'];
        $file_url   = reset($src_img);
        $file_md5   = md5($file_url);

        $download  = new WC_Product_Download(); // Get an instance of the WC_Product_Download Object

        // Set the download data
        $download->set_name($file_title);
        $download->set_id($file_md5);
        $download->set_file($file_url);


        $downloads[$md5_num] = $download; // Insert the new download to the array of downloads

        $product->set_downloads($downloads); // Set new array of downloads
    }
}

Code goes in function.php file of your active child theme (or active theme). Tested and works.

You could also check if product is downloadable using is_downloadable() method in an IF statement on start inside the function.