As you want to "turn off" a background environment and (all?) footnotes, this is not quite the same as Commenting out large sections, although in the end it is very similar.
The easiest way to do this is to define a new "switch statement" using
\newif\ifComplete
You can then use \ifComplete to decide whether to print or hide text. Using \ifComplete and the environ package you can define a background environment that will ignore its contents after \Completefalse. To define \footnote you can "save" a copy of the "real" \footnote command with
\let\realfootnote=\footnote
and then redefine \footnote so that it will ignore its contents after \Completefalse. As \footnote takes an optional argument we might as well support this to.
Putting this all together, I think that the following code does what you want:
\documentclass{article}
\usepackage[textheight=20mm]{geometry}% for display purposes only
\newif\ifComplete% if true print the whole document
\usepackage{environ}
\NewEnviron{background}{\ifComplete\BODY\fi}% print only when \Completetrue
\let\realfootnote=\footnote% save a copy of the original \footnote
\renewcommand\footnote[2][\relax]{% hijack footnote
\ifComplete% print foot notes only in complete document
\ifx#1\relax\relax\realfootnote{#2}\else\realfootnote[#1]{#2}\fi%
\fi%
}
\begin{document}
\Completetrue
\begin{background}
This is some background material
\end{background}
This is some normal text with a footnote\footnote{What a lovely footnote!}
\end{document}
In the WME, \Completetrue means that everything will be printed, so this produces:

If we change \Completetrue to \Completefalse then the output is:

\inputbut some alternative command as\xxx(Add\let\xxx\inputin preamble, then\xxx{filename1} ..\xxx{filename2} ...in the document body. For the short version, simply add a line to the preamble with\renewcommand\xxx[1]{}and comment it with%to return to the long version. – Fran May 27 '17 at 04:20multiaudience. – TeXnician May 28 '17 at 07:45