How to copy from one file to another?
Use the read command!
Copy the entire file into the current file
:read some_file.txt
Copy the first 20 lines
:read !head -20 some_file.txt
Copy the last 20 lines
:read !tail -20 some_file.txt
Copy from some random place in the file
:read !sed -n 30,50p some_file.txt