If you want to add custom fields on your Magento checkout and registration pages, you can use Magento add field to order extension which lets you add 9 types of custom fields such as Text Box, Date, Text Area, Checkbox, Radio Button, Multiple select, Dropdown etc. You can add custom fields to any section of the checkout page. 

Features:

  1. Assign custom checkout fields to specific products or categories to make it visible on that particular product/category.
  2. Restrict checkout fields to specific customer groups.
  3. Display custom checkout fields on emails and PDFs.
  4. Set the position of the custom fields according to your requirement.
  5. Unlimited options for dropdown and Multi select fields. 

More Info: Magento Add Field to Order Extension