Hello,
Here's a support article which explains how to add attachments to Secure Notes: https://support.logmeininc.com/lastpass/help/manage-your-secure-notes-lp050001
Attachments are supported on all web browser add-ons and platforms, including the Premium user iOS and Android mobile apps. However, attachments cannot be opened from the Online Vault in a web browser (i.e., logging in to https://www.lastpass.com).
For more information on downloading your secure notes attachments please see here: https://support.logmeininc.com/lastpass/help/about-downloading-attachments-for-secure-notes