Download Monitor and WP ALL Import - Attach PDF files to download CPT to make them downloadable.

attached_pdf_to_downloadable_file.php

<?php
    // Start preparing an array to insert Download Monitor's Download Version (which is a CPT with Download as parent post).
		$dlm_download_version = array(
			'post_title'  => 'Download #' . $download_id . ' File Version',
			'post_type'   => 'dlm_download_version',
			'post_status' => 'publish',
			'post_parent' => $download_id,
			'post_author' => $attachment->post_author,
		);

		// Insert if no download version already exists.
		$dlm_download_version_id = wp_insert_post( $dlm_download_version );
			
		if ( $dlm_download_version_id ) {
			// Initialise version field with an empty value.
			update_post_meta( $dlm_download_version_id, '_version', '' );

			// Attachment full path in an array.
			$pdf_files = array( $filepath );
			// We need to process the PDF files array using JSON encode as per Download Monitor's data structure requirements.
			$encoded_files = json_encode( $pdf_files, JSON_UNESCAPED_UNICODE );
			update_post_meta( $dlm_download_version_id, '_files', $encoded_files );

			// I have used Download Monitor's file manager service to get file size.
			$filesize = download_monitor()->service( 'file_manager' )->get_file_size( $pdf_files[0] );
			update_post_meta( $dlm_download_version_id, '_filesize', $filesize );

			// Saving empty values in other fields.
			update_post_meta( $dlm_download_version_id, '_md5', '' );
			update_post_meta( $dlm_download_version_id, '_sha1', '' );
			update_post_meta( $dlm_download_version_id, '_sha256', '' );
			update_post_meta( $dlm_download_version_id, '_crc32', '' );
			update_post_meta( $dlm_download_version_id, '_download_count', 0 );
		}