The preset you choose when you create a project sets the frame and pixel aspect ratios for the project. You can’t change these after you save the project file, but you can change the pixel aspect ratio that Adobe Premiere Pro assumes for individual assets. For example, if a square‑pixel asset generated by a graphics or animation program looks distorted in Adobe Premiere Pro, you can correct its pixel aspect ratio to make it look right. By ensuring that all files are interpreted correctly, you can combine footage with different ratios in the same project and generate output that doesn’t distort the resulting images.