Marginalize is a simple plugin for Notepad++ which enables soft wrapping at a specified width.
To install Marginalize, download Marginalize-1.0-x86.zip or Marginalize-1.0-x64.zip, depending on whether you're using 32-bit or 64-bit Notepad++. Unzip the file to a folder named Marginalize (the name must be exactly this, or Notepad++ will not load the plugin) and copy that folder into the plugins folder where Notepad++ is installed. You can find the plugins folder by selecting Plugins | Open Plugins Folder... from the main menu in Notepad++.
The Enable option on the plugin’s menu enables or disables setting padding to establish the specified width for soft wrapping. If Word wrap is not enabled in Notepad++, it will be enabled when you enable Marginalize.
The Settings... option on the plugin’s menu allows you to set the maximum width in characters that you want to display, wrapping any longer lines. The width of a capital “M” is used for reference, in case you are not using a fixed-width font. The default width is 80 characters.
You can check the Center the workspace box to set equal padding on both sides; otherwise, the left padding will be the same as set in Notepad++ at Settings | Preferences... | Margins/Border/Edge | Padding | Left, and the right padding will be set as needed to establish the specified width.