A default WinPE environment is a command prompt and nothing else. To make it useful, you have to "bake" your own image. This process, often called "servicing" the image, involves mounting the WIM file using the DISM (Deployment Image Servicing and Management) tool.
Windows Disk Management is limited. It won't let you move the C: drive partition while you are using it, and it often gets confused by Linux partitions. winpe10 exclusive