Notepad++ does not ship a built-in command that diffs two files. You add that with a plugin. This independent tutorial uses ComparePlus, a file-compare plugin published for current Notepad++ versions and installed from Plugins Admin when the list includes it.
Compare is a plugin
Open Plugins, then Plugins Admin, and look on the Available tab. If ComparePlus is listed, its description in that window is the one to read. If it is not listed, do not download a DLL from a random page. The plugin list changes, and an incompatible DLL will not load.
An older plugin named Compare has also existed. Prefer the entry Plugins Admin shows for your version, and do not mix plugin files from an unofficial Notepad++ build.
Install ComparePlus
- Tick the ComparePlus checkbox. Clicking only the name does not select it.
- Choose Install and let Notepad++ restart.
- If the copy is blocked, start the official Notepad++ as administrator once and install again. The plugin has to match the program’s architecture.
The install tutorial explains Plugins Admin, the auto-updater requirement, and what to do when the menu is missing.
Compare two files
Open the two text files. Open the Plugins menu, open the ComparePlus item, and run the compare command that the plugin shows there. The wording belongs to the plugin, so use the label you see after install.
The plugin highlights how the two documents differ. It does not merge them into a third file unless the command you clicked says it will.
Read the result with care
A compare shows text differences. It does not decide which file is correct. Save any edits yourself with File, Save. If the colors are hard to see in dark mode, adjust the editor theme in Style Configurator, or the plugin’s own settings if it provides them.
Do not replace notepad++.exe to make a compare tool appear. Install the plugin into the official program, or use another diff tool outside this editor.