The Asset Designer toolbox exposes a Folder Search component. For more information, please see the Framework documentation.
The toolbox is your source of the other files you will need when building an asset.
If required, you can use external files, sourced through an external content provider, when building assets. This can be important when considering how to host images in e.g. email offers that use assets.
You can use external files of the following types in asset content:
•Text: text external files only.
•HTML: text, HTML or image external files. You can also use audio and video external files when the HTML asset is to be used in a landing page.