Are you able to convert them to PDF files and password protect them before emailing?
Alternatively, there is other software for CIS that can email them out. they also have integration with QBO for posting the information.
Staffology is a new entrant to the market that i've been checking out - https://www.staffology.co.uk/features/cis-payroll
or a list of other commercially available - https://www.gov.uk/government/publications/construction-industry-scheme-cis-commercial-software-suppliers/construction-industry-scheme-cis-commercial-software-suppliers