There is only one file type that uses the .LMNR extension:
Luminar 2018 Project File
An LMNR file is a project file created by Luminar, a digital photo-editing application. It contains an image that has been edited in Luminar, as well as a record of the edits that have been made to that image. While previous versions of Luminar used LMNR files, current versions of the application do not support LMNR files.
Luminar is a digital photo-editing application that allows photographers to make layer-based edits to their photos. In Luminar 2018, when photographers saved the edits they had made to a photo, Luminar created a Luminar project file (LMNR file). This file contained the edited photo, as well as a record of the layers, adjustments, and other edits the photographer had applied to the photo.
LMNR files could be used to export Luminar-edited photos as .JPG, .TIFF, .PNG, and .PSD files. Current versions of Luminar, however, no longer support LMNR files. Instead, those versions store edited photos and a record of the edits made to those photos in Luminar catalogs, which are comprised of TIFF, .STATE, and .LUMINAR files (among others).
You can open an LMNR file in Luminar 2018. To do so, open Luminar 2018 and selectfrom the program's menu bar.
Updated: September 5, 2020