CTAN update: subfiles
Update v1.2 of the subfiles package makes it compatible with class files and package's that modify the document command (like the revtex4-1 class). Older versions generated errors in such situations. The subfiles package allows the user to structure a document into a main file and one or more subfiles with the twist that the subfiles can be compiled separately, whereby the class and the preamble of the main file is included automatically.
This package is located at http://mirror.ctan.org/macros/latex/contrib/subfiles More information is at https://www.ctan.org/pkg/subfiles
Thanks for the upload. For the CTAN Team Manfred Lotz We are supported by the TeX user groups. Please join a users group; see http://www.tug.org/usergroups.html .
subfiles – Individual typesetting of subfiles of a "main" document
Using subfiles the user can handle multi-file projects more comfortably making it possible to both process the subsidiary files by themselves and to process the main file that includes them, without making any changes to either.