Square to circle transformers are often used for HVAC ducting, fume hoods and hoppers. Traditionally sheet metal workers are taught how to develop patterns on the drawing board and then transfer the pattern to the work piece, but the modern shop is more likely to use laser cutting or CNC nibbling and therefore G code files are generally generated from CAD data. The DXF file format is a favorite of the sheet metal industry because most CAD software will import DXF. Engineer's need properties like volume and centroids. Estimator's need area calculations. Storpro1 is a light-weight and small on memory but a powerful app to run on a Android phone or Tablet. There are no adverts, no in-app billing and no lengthy transfer of data back and forth to cloud servers.
Android users up to Lollipop have to accept storage permissions pre install. Marshmallow and up need to allow storage file permission post install. Here's a video of how it's done with Android Nougart : https://youtu.be/3Vr3N-BTVag