Programs in Windows run in virtual memory space. A process can read its own memory from a given virtual address, or a memory of another running process (given appropriate privileges). There are no methods in .NET Framework to directly read data from an arbitrary physical address.

Say, I know from some program that a certain object is located at a certain physical address in the physical memory. How can I read the byte from that physical address and the subsequent bytes?

A book that I am reading now says that this is usually done by mapping the physical address into the virtual address space of your application.

Which Windows APIs can be used for such a task and how to implement it in a .NET Windows Forms Application?

I am interested in x64 platform only.