The PDF file should always open in the browser if the Adobe PDF Reader plugin is installed but it will still take the same time to open as it will to download. The file size is the same which ever way you do it.
To create a PDF you need Adobe Acrobat Software (not Acrobat Reader) but some professional paint programs also create PDF's)
You can get the icon from anywhere but I would recommend using one of these from the Adobe site (scroll down when you get there. Just copy it using right mouse click then add it to your site.
http://www.adobe.com/misc/linking.html#pdficon
:)