If you want to replace/overwrite the entire file content by pasting the command then you need to followin these steps:
Type ESC to come out of insert mode.
Type the following command and hit the enter key:
:%dThe above command will delete all the lines/content in that file.
Type i to enter into INS mode.
Press CMD + V to paste the new content.
Hit ESC and then type :wq and hit enter key.
You are done with replacing/overwriting the entire file content with Vim.