To provide your clients with larger explanatory notes/leaflets (typically sent via email as PDF attachments), we recommend that you create these as online materials that we can reference via the portal questionnaires.
By way of example, "A leaflet explaining Stamp Duty Land Tax and the appropriate fee payable on a Purchase completion", could be explained in detail via a URL to your corporate website and then referenced at that question in the Purchase Questionnaire. Maintaining these URLs is an easier and more effective way of keeping legislation up to date and informative to your client.
As note of caution : remember to version manage your guidances notes and these URLs. Every URL should remain in place and not be edited. If you did not version stamp these URLs then clients will see the version at that time and not the version they read at the time of their form.