How can I download archive of ubuntu community documentation so that i can use it offline?
wget -r -l 0 -np -e robots=off -U "Mozilla/5.0 (Windows NT x.y; rv:10.0) Gecko/20100101 Firefox/10.0" -k -p -R *action=* https://help.ubuntu.com/community in your target directory. @asutosh 's would hypothetically work, but one would incur robots.txt issues, extra pages downloaded, etc. I have tested this and it will download all HTML. If you want to get images, you may need to do a bit of tweaking.
Just use wget
wget -p --convert-links -r website.com -o logfile to download the whole site and convert the links to have it for offline viewing. Then you can view it offline in html format.
You can then convert it afterwards individually to pdfs or whatever suits you, as it is a hasstle to convert it instantly online while doing.