Using pdf-tools

[Julius Hamilton]

Hey,

I'm a beginner to emacs and I'm trying to get going with the library
pdf-tools.

The documentation says I should add the line "(pdf-tools-install)"
"somewhere in my .emacs.el file".

I noticed that in my home directory I have a .emacs.d file. Some
documentation said people usually have a .emacs file but sometimes also a .
emacs.el file or a .emacs.d/init.el file, as an init file.

I was wondering, what are the reasons for having these different kinds of
init files?

I added "(pdf-tools-install)" at the end of my init.el file, and restarted
emacs. I tried a command from the pdf-tools docs, "M-x pdf-tools-help RET",
which the system did not recognize.

I was wondering if anyone could give me a hand and explain to me why this
is and what a good next step would be. Should I set up my emacs with a
emacs.el init file instead?

Thanks very much,
Julius