which find -exec convert command to use in order to concatenate n pdf files into one?9sa

Question

I have in my linux:

1.pdf 2.pdf 3.pdf 4.pdf ... n.pdf

Which find -exec (with convert command) to use in order to connect all pdf into a single one?

output.pdf

so far i used

convert 1.pdf 2.pdf output.pdf

but i'm trying to have it working for n pdf files.

thanks