Those attachments are generated on the server with the wkhtmltopdf tool. The checkboxes only appear when that tool is installed at the path set in Client Config (Order: Catering tab) under Proposals Print PDF In Server Library Snappy Binary Path (default /usr/bin/wkhtmltopdf). If it is missing or the path is wrong, the email is still sent with the proposal link and any files you attach manually, but without the generated PDFs. Ask Sprwt support to verify the server setup if you expect PDFs to be attached.