Not using WordPress? You should simply be able to skip step 1. If you are using an alternative CMS system you may need to use a similar plugin if you find steps 2 and 3 don't work for you.
Please do not use a plugin to create your iFrame it is not needed and will likely alter the URL code and prevent it from working.
You will need a plugin that allows you to insert PHP to your posts or pages, below is one option that has been tested and works.
Allow PHP in Posts and Pages
Setup is simple, login to your WordPress admin account, go to the Plugins page and search for "Allow PHP in Posts and Pages" the first result should be the plugin you want, Install and then Activate it.
Create a new Page within WordPress to hold your e-Sign page. Insert the following URL within an iFrame:
http://systemname.opencrm.co.uk/portal/index.php?option=com_ocrm_soquicksign&order_number=[php] echo $_REQUEST['esignid'];[/php]
So for example