I've customized fields in an opportunity. Within a workflow when an opportunity reaches 100% I send automatically an email using the custom fields. I need to attach automatically a file (or several) to this email within the workflow. How can I do that?
Or you can use Visualforce email template to dynamically add attachments. For that you will need code as well. This will still have its own limitation and you need to generate file at runtime.
If you want to send pre created attachment in email then I suggest you to go by Trigger/Apex to send email where you can send any attachment with the emails. Also if you are sending emails to internal users then it will not be counted againest your limit.