I don't manage to install pd extended on lubuntu OS.
I try the first method in the terminal presented here :

but after entering this line

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-key 9f0fe587374bbe81

I've got this answer :
failure to receive from the server Tags: keyserver error

also, pd don't appear in the library of software installed with Lubuntu

any idea