A pls file extension is related to the Pro/ENGINEER (Creo Elements/Pro) and used for its temporary files.
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.PLS file extension - Pro/ENGINEER temporary data
What is pls file? How to open pls files?
File type specification:
The pls file extension was also used for one of the temporary files in Pro/Engineer program.
Temporary files may be created by computer programs for a variety of purposes; principally when a program cannot allocate enough memory for its tasks, when the program is working on data bigger than architecture's address space, or as a primitive form of inter-process communication.
The default software associated to open pls file:
Pro/Engineer (Creo Elements/Pro) 
Company or developer:
Parametric Technology Corporation
Pro/Engineer is integrated 3D CAD/CAM/CAE solution used to mechanical engineering, design and manufacturing. First version was released in 1997. Pro/Engineer runs on Microsoft Windows and Unix. In 2010 Pro/Engineer was renamed on Creo Elements/Pro.
List of recommended software applications associated to the .pls file extension
Recommended software programs are sorted by OS platform (Windows, macOS, Linux, iOS, Android etc.)
and possible program actions that can be done with the file: like open pls file, edit pls file, convert pls file, view pls file, play pls file etc. (if exist software for corresponding action in File-Extensions.org's database).
Unspecified and all other actions for computer programs working with pls file - Pro/ENGINEER temporary data
Click on the software link for more information about Pro/Engineer (Creo Elements/Pro). Pro/Engineer (Creo Elements/Pro) uses pls file type for its internal purposes and/or also by different way than common edit or open file actions (eg. to install/execute/support an application itself, to store application or user data, configure program etc.).
