There are numerous ways one can convert a web page (HTML) to PDF. Some using websites, a Firefox addon, but here is how to do it in Linux.
You could just, select "Print" (in Firefox: File > Print) and then select "Print to file" and the output "PDF".
To install wkhtmltopdf in Ubuntu, run the following command in a terminal:
sudo apt-get install wkhtmltopdf
Then, to convert a webpage to PDF, open a terminal and type this:
wkhtmltopdf http://www.webupd8.org webupd8.pdf
Replacing http://www.webupd8.org and webupd8.pdf with the website you want to convert to PDF / the name you desire for the converted PDF file.
The output of wkhtmltopdf is pretty good. Take a look: