Create a folder somewhere. Call it "New documents" or something. Create blank text file(s) of the type you want within that folder. For example, I have a blank

Create a folder somewhere. Call it "New documents" or something. Create blank text file(s) of the type you want within that folder. For example, I have a blank.txt which opens in TextMate, a blank.rb which opens in TextMate, and a blank.rtf which opens in TextEdit. Lock the folder (by selecting it, Cmd-I, check "Locked"). Put the folder in your Dock. Hey presto. You can now create a blank text file anywhere simply by dragging it out of this folder in the Dock. Because the folder is locked, you won't delete the original - macOS will make a copy for you, every time. Just rename it before opening and you're done.