I have a Acer PC running Windows 10
The laptop has three partitions: C, D and E.
If I install Ubuntu, I want it to install in C drive and not erase the data on the other two drives.
It is OK for me if the contents of C are deleted.
Will Ubuntu respect the existing partitions or format all the drives?
Yes, it's possible. However, you cannot install Ubuntu on a Windows partition (C), you will have to either delete the Windows partition (which means that Windows will be completely gone and replaced with Ubuntu), or shrink the Windows partition in order to make space for an additional Ubuntu partition.
During the installation, Ubuntu will offer you a choice of where to install it, and weather to replace Windows or install Ubuntu alongside Windows, choose "Something else" here:
This will give you something like the the following screen; although in your case you'll probably have fewer partitions:
Here, you can either resize the main Windows partition and make it smaller, and then create a new Ubuntu partition in the free space, or entirely delete the Windows partition, and create an Ubuntu partition in the free space. Ubuntu will not touch your other two partitions unless you tell it - but do be careful with what partitions you delete. It's also recommendable to always have a backup.
See also How to use manual partitioning during installation? for more details.
