Click "Attach a File" and select the PDF file you want to attach; click "Open" to add the attachment to your message. Click "Send" when you are ready to send the email.

We show how to add (and send) photos, videos, text documents and other files as email attachments, using the Mail app on your iPhone ...

So, what you need to do now is simply send an email to the Kindle email ID with the PDF file attached to it. Also, you can send multiple PDF files at the same time, as it is with any email client.

“Is there any way to password-protect and lock a sensitive PDF file before sending it as an attachment through email? I cannot afford Adobe Acrobat Pro and free primopdf didn’t work for me ...