The Exclude Pages plugin adds a checkbox, “include this page in menus”, which is checked by default. If you uncheck it, the page will not appear in any listings of pages (which includes, and is usually limited to, your page navigation menus).  To use this plugin, do the following:

1. Go to your blog Dashboard
2. Click on Plugins > Installed
3. Activate the “Exclude Pages” plugin

Once this plugin is activated, you can chose to exclude any page on your blog from being listed in your page widget by doing the following:

1. Create/edit a page on your blog
2. In the right sidebar of the Edit Page UI, deselect “Include this page in user menus” to prevent it from being listed in your sidebar widgets

Let us know if you have problems/questions.