Ubuntu and Windows 10

Now I have Ubuntu as a dual boot with win 10 on my device... Can I view my hard disk partitions D, E... on Ubuntu without losing the data on them? and if I can't what is the alternative if I want to fully migrate to Ubuntu without losing my data

Risk of data loss is never 0%, especially when you are installing or uninstalling operating systems or making changes to partition tables. Even experienced users make mistakes sometimes. You should always have a backup plan in case something goes wrong (and a plan in case your backups fail too!)

Ubuntu does not refer to volumes with letter assignments. This is a Windows-only convention. Ubuntu natively supports NTFS partitions, so all you need to do is mount the partition and you can read and write data to those volumes.

The "Disks" application included with Ubuntu is a GUI application that is easy-to-use to view and manage disks and partitions on your computer. Mounting a partition is as easy as selecting it and clicking the icon ▶️. It will also show you the absolute path where the disk is mounted so you can find it in your file manager, file picker, and other applications.

If you are dual-booting Windows and Ubuntu, you must disable "Fast Startup" in Windows. Otherwise Windows will use a hybrid suspend instead of shutting down and your file systems will mount as "read-only" in Ubuntu.