This is a requirement, for example, if one is preparing the proceedings of a conference whose papers were submitted in LaTeX.
The nearest things to canned solutions are Peter Wilson’s combine and Federico Garcia’s subfiles classes, but many approaches have been proposed. Each of of the offerings has its own advantages; in particular, several distinctly light-weight solutions (for example, includex and docmute) are available, well-suited to less formal documents.
Combine defines the means to ‘\import’ entire documents,
and provides means of specifying significant features of the layout of
the document, as well as a global table of contents, and so on. The
complete set of facilities is pretty complex. An auxiliary package,
combinet, allows use of the \titles and \authors
(etc.) of the \imported documents to appear in the global table
of contents. The basic structure of a combined document would be:
\documentclass[...]{combine}
...
\begin{document}
...
...
\begin{papers}
% title and author of first article,
% to go the the main ToC
\coltoctitle{...}
\coltocauthor{...}
\label{art1}
\import{art1}
...
\end{papers}
...
...
\end{document}
The subfiles class is used in the component files of a multi-file project, and the corresponding subfiles package is used in the master file; so the structure of the master file looks like:
\documentclass{}
...
\usepackage{subfiles}
...
\begin{document}
...
\subfile{subfile_name}
...
\end{document}
while a subfile has the structure:
\documentclass[mainfile_name]{subfiles}
\begin{document}
...
\end{document}
Arrangements may be made so that the component files will
be typeset using different page format, etc., parameters than those
used when they are typeset as a part of the main file.
A more ‘raw’ toolkit is offered by Matt Swift’s includex and newclude packages, both part of the frankenstein bundle. Note that Matt believes includex is obsolete (though it continues to work for this author); furthermore, its replacement, newclude remains “in development”, as it has been since 1999.
Both includex and newclude enable you to
‘\includedoc’ complete articles (in the way that you
‘\include’ chapter files in an ordinary report). The preamble
(everything up to \begin{document}), and everything after
\end{document}, is ignored by both packages. Thus the
packages don’t “do the whole job” for you, though: you need to
analyse the package use of the individual papers, and ensure that a
consistent set is loaded in the preamble of the main report. (Both
packages require moredefs, which is also part of the
bundle.)
A neat (and simple) toolkit is offered by the
docmute package; once the package is loaded, anything
between \documentclass[...]{...} and
\begin{document} in an \input’ed or \include’d
document is ignored, and then the input is processed up to
\end{document} in the input file. The package does nothing
about \usepackage (or anything else) in the preamble of the
included document; it’s up to the user to ensure that any packages
needed are loaded, and any other necessary configuration is done, in
the parent document.
The standalone package develops on the ideas of docmute; it was designed to meet the needs of users who are developing images from one of the more extreme new graphics packages (notably pgf/tikz) where the compile time of the graphics is such that separate compilation is very desirable. Standalone provides a means of developing the graphics in a convenient way, detached from the development of the document as a whole; its value for use in multiple documents is clear.
The user includes the standalone package in the main document, and each subfile uses the standalone class. (Standalone uses article for the “real” work in stand-alone mode, but it may be asked to use another).
The real difference from the docmute package is flexibility. In particular, you can ask that the preambles of the included documents be gathered up, so that you can construct a good preamble for the master document.
A final “compile-together” approach comes from the subdocs
package. The driver file contains a \subdocuments command:
(the optional arguments provide layout options, such as control over whether\subdocuments[options]{file1, file2, ...}
\clearpage or \cleardoublepage are used between the
files). Each of the sub-files will execute
to declare the name, master, of the calling file; each of the subfiles reads all the\usepackage[master]{subdocs}
aux files, so that
tables of contents may be produced.
A completely different approach is to use the pdfpages
package, and to include articles submitted in PDF format into a
a PDF document produced by PDFLaTeX. The package
defines an \includepdf command, which takes arguments similar to
those of the \includegraphics command. With keywords in the
optional argument of the command, you can specify which pages you want
to be included from the file named, and various details of the layout
of the included pages.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=multidoc