Email attachement parameter

Dear all,

In Designer/Process Orchestration I have a custom process that sends an email to new users. I want to include an attachment in the email. For this I'm using the "Attachement" parameter and I'm setting it like "C:\IAM.pdf", but I'm getting a warning message saying it can't find the file. 

Do you have any suggestion? The file should be in a specific folder? Or does the path need to have a specific format?

Thank you,

Martina