Create post, add attachment and update field via ACF

import_files.php

<?php

/*
 *
 * This small scripts creates a post and attaches a file using Advanced custom field.
 * 
 * Created by Miguel Garrido 
 * miguel.co.nz | miguel@blacksheepdesign.co.nz
 *
 * Notes: 
 *
 * The purpose of this GIST is for reference only as it may be helpful for you.
 *
 * Further reading and references:
 *
 * http://codex.wordpress.org/Function_Reference/wp_insert_attachment
 * http://www.jqui.net/wordpress/acf-upload-image-made-easy/
 * http://stackoverflow.com/questions/15638046/how-to-upload-an-image-on-acf-with-update-field-on-wordpress
 *
 */

class import {

	public static function init(){

		$files = self::get_files();

		for($i = 0 ; $i < sizeof($files) ; $i++ ){

			// Base url to test if file exists
			$base_url = '/full/path/to/file/';
			$_full_file_url = $base_url . $files[$i]->file;
			
			// File url under wp-content/uploads/
			$file_url = 'docs/' . $files[$i]->file;
			
			// Test if file exists
			$file = fopen( $_full_file_url , 'r' );
			if( $file !== false ){
				
				// Display on screen, just for fun
				echo 'Creating post: ' . $files[$i]->name . '<br />';

				// Posts arguments for our new post
				$args = array(
					'post_title' => $files[$i]->name,
					'post_type' => 'resources',
					'post_status' => 'publish',
					'post_content' => $files[$i]->desc
				);

				$new_post = wp_insert_post($args);

				// Add the file we will update
				$att = self::update_attachment( 'file', $new_post , $file_url );
				
				// This is part ACF: field_5590967110b9f is our key 
				update_field('field_5590967110b9f',$att['attach_id'], $new_post );
			}

		}

	}
	
	// Update attachment file
	public static function update_attachment( $f, $pid, $file_url ){
		
		wp_update_attachment_metadata( $pid, $f );
		
		if( empty( $file_url ) ) 
			return false;

		$wp_upload_dir = wp_upload_dir();
		$filetype = wp_check_filetype( basename( $file_url ), null );

		// Prepare an array of post data for the attachment.
		$attachment = array(
			'guid'           => $wp_upload_dir['url'] . '/' . basename( $file_url ), 
			
			'post_parent' 	 => $pid,
			'post_title'     => preg_replace( '/\.[^.]+$/', '', basename( $file_url ) ),
			'post_type' 	 => 'attachment',
			'post_content'   => '',
			'post_status'    => 'inherit',
			'post_mime_type' => $filetype['type'],
		);

	  	$attach_id = wp_insert_attachment( $attachment, $file_url );

		return array(
			'pid' => $pid,
			'url' => $file_url,
			'attach_id' => $attach_id
		);

	}

	// Our files data (name, description and file_url) were in another database and this info was important to keep
	public static function get_files(){

		if( is_user_logged_in() ){

			$old_db = new wpdb(DB_USER, DB_PASS, DB_NAME, DB_HOST);
			$old_db->show_errors();
			
			// This was my query, it does not mean your query will need to be like this
			$files = $old_db->get_results( "SELECT p.file as 'file', p.name as 'name', p.description as 'desc', p.user_id as 'user_id' FROM wp_documents p" );

			return $files;
			
		}

	}

}

/* Run with 
 *
 * import::init();
 *
 */