Protect PDF's upload step accepts only one PDF at a time (isMultipleInput is false), matching a single email attachment being password-protected before sending.
Sending a PDF's password in the same email as the encrypted attachment undermines the protection, so the password should be shared through a separate channel. Encrypt PDFs for Secure Email Communication: Complete Guide - TitanFile
Protect PDFPassword Protect PDF Before Emailing
Add the invoice or contract you plan to email.
Enter a strong password for the document.
Adobe's official guide explains setting a password to view or edit a PDF in Acrobat before sharing it. How to password protect PDFs - Adobe
Download the encrypted PDF file.
Sharing the Password Securely
Send the password to the recipient via a separate communication channel.
Attach the encrypted PDF to the email.
Handling Multiple Documents
Click the start-over control on the results screen.
Upload the next PDF file.
Continue with Owner vs User Passwords or AES 256 Compatibility.
Frequently Asked Questions about Password Protect PDF Before Emailing
Should I use the same password for every recipient?
Choose a distinct password for each sensitive document you email.
Can I text the password instead of emailing it?
Consult your recipient about their preferred channel for receiving a password.
What file types can I protect this way?
Save your document as a PDF before starting this workflow.
How do I know the attachment is actually encrypted?
Try opening the downloaded file without entering the password first.