The topic heading is enough!
In edit mode, press
Ctrl+H for replace. This will show a “Find and replace” dialog at the bottom of the panel. Just enter the things as usual, how it works is pretty intuitive.
There is replace for a single file as described above, but not globally.
Here’s the feature request for global replace https://forum.obsidian.md/t/mass-search-replace/4395
Oh forgot to mention the word ‘automatic’ before ‘text’.
I was seeking a automatic text replacement feature, which replaces text to another preset text as you type.
No there is nothing like that in Obsidian at the moment.
There might be something in your operating system. What OS are you using? For example, MacOS has text substitution in the Keyboard -> Text preferences.
I’ll rename the topic for clarity.