I understand that HTTPS protects data in transit from eavesdropping along the way. A couple of questions:

Would documents such as PDFs that are downloaded off my site also be encrypted using https?

I wouid like my business friends to be able to download information securely without needing to install any new software on their systems. For what I'm doing just "average" security is fine. Would HTTPS be the answer and is it easy to set up? Thanks for any perspectives.

A download is a binary operation.

It is the form data that is encrypted "in flight", so only the request for the file would be encrypted.

There is also a bug in IE with HTTPS: downloads http://support.microsoft.com/kb/812935

What kinds of binary files can be downloaded from a website? In other words, can I create a link on my webpage to any type of binary file or only certain types?

Any file type can be linked, if the file is a server processable file (.htm .html .php .asp) etc it will be processed and the result served out, if not, it will be presented to the client as downloadable.

I see. So a client could obtain any kind of encrypted file from a website using an ordinary browser. Of course, they might need additional software on their system to process the file. Too bad Macs and PCs don't provide a common, basic kind of encryption system in the OS. Wouldn't have to be strong encryption for what I need.

So a client could obtain any kind of encrypted file from a website using an ordinary browser

Yep, always assuming they know where the file is.