when i am trying to create one email to send the pdf to the customer 
but, the customer ask I need a password pdf when I am clicking pdf will be ask password and open it .....any clue?

The WarehouseCalloutService class does not appear to have run successfully. Make sure that you run this class at least once before attempting this challenge. Since this class is implementing the queueable interface, you may want to wait to ensure that it has processed successfully.
 THis Error will be occur how this solve 
my time i will be test the program but error occur

when i am trying to create one email to send the pdf to the customer 
but, the customer ask I need a password pdf when I am clicking pdf will be ask password and open it .....any clue?

when i am trying to create one email to send the pdf to the customer 
but, the customer ask I need a password pdf when I am clicking pdf will be ask password and open it .....any clue?