An RPLN file is a plugin file used by the page layout program, InDesign, that creates page design and also porvides print publishing. it contains functions that are required to run and is located in a Required directory where the InDesign software is installed.
RPLN File Format
RPLN files are saved in InDesign proprietary file format and there is no further details about the internal file structure of RPLN files.
About Adobe InDesign
Adobe InDesign is a professional desktop publishing software application that is widely used for creating print and digital media. InDesign supports the use of plug-ins, which are additional software components that can be added to extend the functionality of the program.