I need to set a PDF file limit to be 5 MB. Is there a way to create this restriction? Is there a code I can insert into the actual uploads icon to set individual attachment file size limits?

You can set a file-size limit in your HTML page. There's no need to have a double-check... Inside the PDF file it's more difficult to implement such a control because the file-size doesn't change until you actually save the file, so someone can attach multiple files, click the "Validate File Size" button and get a positive reply, but then when they actually save the file it will go beyond 5MB and the web-site won't accept it, which is annoying.