Infowise Document Link Field can link items to documents located in the same library, a custom field that enables adding link to existing document in document libraries in the site collection.

Installation
Note: as the product is installed as a SharePoint Solution, you need to install it only once, regardless of the number of your front-end servers.
Run the installation package from one of your front-end server machine and follow the on-screen instructions. You do not have to change the default settings.

Requirements:
* SharePoint

The license of this software is Free Trial Software, the price is $249.00, you can free download and get a free trial.