If your email contains password protected PDF attachments and you are generating a single one PDF document (by merging all attachments to one PDF file), you will be prompted to enter the password of the PDF attachment to continue. If you don’t want know the password or simply want to exclude such password protected PDF attachments, you can go to Outlook > Email to PDF add-in toolbar > Output Settings > Others (last) tab, and enable the option ‘When merging, ignore Password prompt on PDF attachments‘.
Enabling this will force the add-in to ignore password protected PDF attachments (if any in the email) from being included in the PDF export.
For more information, refer to the product page at https://www.assistmyteam.com/email-to-pdf-for-outlook/