The iManage FileSite application doesn't appear to be available anymore. I've checked its website, and although various products that have iManage in their name are available, the FileSite is missing.
This means you will have to get in touch with the developers in order to obtain additional information related to the availability of FileSite and its integration with 3rd party products.
Access their website then click on the right Contact Us button that is attached to the page: https://imanage.com/products-solutions/