Is there a way to do this in Notepad++ while using plain text files? It would require that Notepad++ identity certain sequence of characters as being a link to another line or marker in the file.

Пример текста можете привести?

Notepad++ is a text editor, not a word processor.

However, if you’re doing things like code, the builtin feature Function List (enable using the View > Function List menu entry) will allow you to see go immediately to function definitions.

Using the same Function List feature, this post shows the config information that goes into %AppData%\Notepad++\functionList.xml, which allows the Function List to work with Markdown text headers (so you can quickly navigate between sections in your Markdown documentation).

If you define a UDL, then define the Function List setting to accompany it, you could get a table-of-contents-like feature for whatever style of text you have (whether it’s code, Markdown, TODO list, or what have you).

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See @MAPJe71’s excellent FAQ Desk: Function List Basics in the FAQ section of the forum for more on how to configure new languages/formats to be visible in the Function List.