Can someone please explain how I can attach a form/document to text in a K2 item, users should be able to key in and save the information.

Hi. This is not something that can be done through configuration. You need to find/develop a K2 plugin for that.

Do you know of a suitable plug in please?

It depends on what exactly you want to achieve. You can always search at the K2 extensions directory at getk2.org/extend . If you are familiar with programming you can create your own plugin. You can get started by looking at the example K2 plugin code at github.com/joomlaworks/example-k2-plugin/ .