This can be done by setting up a right-to-work category, a document can then be uploaded against this.
You can do this, if you follow the below steps:
Find the employee using the organisation search then click Person.
Click Profile then go to Eligibility to Work.
Click Edit then select the 3rd option.
An additional documents option will then appear. You can tick any of the options to upload a document. If you would like to change the options that you see, follow the below steps:
Click on Configuration and then click Settings.
Click Module Settings and then click on HR.
Click Work Eligibility / Identification.
You will see the screen where all specific settings can be set.
Click into the option then select Check type N.
Select Document entry, e.g. Generic document upload means that you will have the ability to upload a document.