Can I read PDFs on my Kindle Fire?

Normally yes -- you could download a PDF file into Kindle Fire by navigating to your email account Kindle Fire's webbrowser Silk and downloading the file normally into the Kindle.

However, my ebooks have a security password protection against copying the content, so you will not be able to open the PDF file at all and will get a message like this: Invalid Item — This item is protected with DRM and cannot be read on your Kindle. Please remove the item from your device and download it again or purchase a copy from the Kindle Store.