How to read virtual memory using winapi?

Question

C++ / C#

Winapi task: Develop a DLL with a function that searches the entire virtual memory for a given string and replaces it with another string.
How can you read the entire virtual memory and look for a string in it, and then also replace it? Or at least how can you access the entire virtual memory of a process and replace a string in it? Then you can inject the dll into all processes. And in them she will do all the work.

Answer 1

Kind of a tricky job. Cheats/trojans/etc?
VirtualQueryEx - query memory pages, ReadProcessMemory - read memory, WriteProcessMemory - write.