Allow permissioned contact to download the invoice
To Print other contact Invoice Logged in contact need 'access CiviContribute' permission
To Print own Invoice Logged in contact need 'view my invoices' Permission.
If user role only have 'view my invoices' permission and want to print invoice of contact which have Permissioned relationship. It gives access denied message.
(e.g. Employee should print invoice of Employer contact if relationship is Permissioned)
To upload designs, you'll need to enable LFS. More information