A lot of the pre-managed disk documentation has become hard to find. Below is a cheat-sheet on where to find the documents you need to work with Azure ARM VMs, images, and storage accounts.
Create an Azure VM from custom image (VHD) – https://docs.microsoft.com/en-us/azure/virtual-machines/windows/sa-upload-generalized
Create an Azure VM from existing VHD – https://docs.microsoft.com/en-us/azure/virtual-machines/windows/sa-create-vm-specialized
Create an Azure VM Image (and VM) from existing Azure VM – https://docs.microsoft.com/en-us/azure/virtual-machines/windows/sa-copy-generalized