How to autocomplete substring of the file.

[irfan-hossain-bhuiyan]

Let's say I have a text file with a lot of text in it. As usual I have a lot of repeated words.While typing a word,I want neovim will find the substring in the current file,and suggest word by it. As example :
procastination is a bad habit.

After it when I will type pro I would be suggest procastination in the autocomplete.
As I know coc.nvim do this thing by default. Is there any way to do it in here? It is very useful for editing basic text file,or any string in a programming language.

[VonHeikemen]

In the autocomplete documentation there is an example on how to enable that behavior in nvim-cmp: Autocomplete - adding a source