This article explains what an ATOM file is, how to open it, and how to convert it to another format.
Getting Started with Python in Atom | Python with Atom Editor
A file with the ATOM file extension is an Atom Syndication Format file that is saved as a plain text file and formatted as an XML file.
ATOM files are similar to RSS and ATOMSVC files in that they are used by frequently updated websites and blogs to publish content to Atom feed readers. When someone subscribes to an Atom feed through a feed reader tool, they can stay up-to-date on all the new content that the site publishes.
While it is entirely possible to have an .ATOM file on your computer, it is unlikely. Typically, you will only see ".atom" when it is added to the end of a URL that uses the Atom Feed file format. From there, it is less common to save the ATOM file to your computer than to copy and paste the Atom feed link into your feed reader program.
