Karrde

Includes a file’s contents in the widget. Quick and dirty, all this does is use the PHP include function to include the specified file in the widget. There is NO checking done whatsoever on the file, so use it at your own risk. I wrote this because I couldn’t find a widget to do this ? plugins exist for using include in posts and pages, but not in widgets.

Include Widget

Includes a file's contents in the widget.

redpixelstudios

The RPS Include Content plugin is useful when you need to include the same content across many posts or pages. For example, you may want to place your company boilerplate at the bottom of press releases in your News section. Instead of pasting the boilerplate copy at the end of each of these pages, you can now insert the shortcode (along with the post ID, and for multisite configurations, the blog ID) where that content should appear.
When you modify your source copy, changes will appear on all pages that contain the shortcode. There’s no need to open and modify multiple pages.
When a user previews the post from the WordPress Administration, the included content is distinguished with an on-hover highlight. A link is provided so that the source content can be conveniently accessed and modified. The preview of the include will not distort the target page – the width, height and position will remain as defined by the site.
To easily obtain the blog ID and post ID, install the free <a href="https://wordpress.org/extend/plugins/rps-blog-info/" rel="ugc">RPS Blog Info</a> plugin, which places that information (and much more) on your WordPress 3.3 Toolbar.
<h4>Features</h4>
<ul>
<li>Include featured image of the included post with optional wrapper and custom class.</li>
<li>Allows specific shortcodes to display within included posts.</li>
<li>Allows oEmbeds to display within included posts.</li>
<li>Respects the more tag in posts automatically.</li>
<li>Set the length of the content to be displayed by word count.</li>
<li>Option to remove the hover interface.</li>
<li>Option to include private content.</li>
<li>Display the title of the included post without any content.</li>
<li>Include the title of the included post with or without a hyperlink.</li>
<li>Include a page or a post in another page or post.</li>
<li>Specify whether the content or the excerpt should be used.</li>
<li>Updates made to source content are reflected on all target pages.</li>
<li>Source content pulled into a page is easily distinguishable and accessible when viewing the page on the front-end while logged into the WordPress back-end.</li>
<li>Protects against generating include loops and calling nonexistent source content.</li>
<li>Displays errors on the front-end to logged-in page/post editors.</li>
<li>Compatible with single and multisite installs.</li>
<li>Support for password protected posts.</li>
<li>Strip shortcodes from included posts.</li>
<li>Default Settings page.</li>
</ul>

RPS Include Content

Makes it easy to pull content from one post or page and place it on another using a simple shortcode, even in a multisite environment.

Include Widget vs RPS Include Content