A file with .xd extension is a mockup created for website or mobile applications using the Adobe XD software. Designers, creative teams, and organizations use these files to design applications by referring these. A single XD file contains design elements such as images, shapes, and text that provide complete feature set to develop fast and intuitive wireframe prototypes for developers to start developing these as applications.
XD File Format
XD files contain graphic elements (image,s shapes, and text) in layers as one or more artboards. These along with guides and layers provide the building blocks for the wireframes.
Artboards - These represent the screens in an application or pages of a website, and streamline the design processes. An artboard creates interactive designs for multiple screen sizes in a single document.
Guides - These are used to line up objects or manage spacing between elements on an artboard. Guides use grids that serve as a framework to organize design elements (images, glyphs, paragraphs) and ensure the symmetry of the layout.
Layers - UX designers use layers in XD in the same way as using these in Adoble Illustrator or Photoshop. These are used to organize the work on artboards in order to avoid clutter and are controlled from the Layers panel.