In your automation for sending the email, there is an “Attachments” section. In that section, you can choose your attachment field that contains the PDF file.
If the PDF file lives in a different Airtable record than the record that is triggering your automation, then you will need to perform a “Find Records” action to find the record that contains the PDF file, and then you can insert the results of the “Find Records” action into your send email step. You would need to choose the “flatten” option after you choose the attachment field from the “Find Records” action.
If the PDF file lives in a different Airtable table/record than the table/record that is triggering your automation, then you will need to perform a “Find Records” action to find the record that contains the PDF file, and then you can insert the results of the “Find Records” action into your send email step. You would need to choose the “flatten” option after you choose the attachment field from the “Find Records” action.