I have got a workflow. The workflow is sending emails. How can i attach pdf document to my auto mail?
Not clear if this question is about SharePoint Online or SharePoint on-premise (SP2007-2016). Let me provide you with some options.
SharePoint Designer workflows: It is not possible to do this with the out-of-the box workflow actions. You can send an email, but not add an attachment.
Nintex Workflow: If you happen to have Nintex Workflow installed in your SharePoint environment then you can use their email facility. It supports attachments.
Microsoft Flow: If you are using SharePoint Online, or have setup the Data Gateway (to use Flow for SharePoint on-premise), then you can use the Microsoft Flow facility to send emails, including attachments. I wrote a blog post some time ago about how to mix SharePoint Designer workflows and MS Flow to send attachments. Have a look here.