When viewing InDesign files from the File Overview page, you will have the option to preview the document within your browser window. To do so, select the 'View Document' icon.

This will launch a preview of the PDF file contained within the zipped package. You can view individual pages of the document, download the PDF file, and print the file from the preview window.

To download the InDesign document select the 'Sizes' tab from the File Overview page, then select the 'Download Size' icon for the 'INDESIGN Original' image size. 

Select 'Start Downloading' from the following window that appears. This will add a zipped package to your downloads folder containing the .INDD file.

After opening the .INDD file, the images will not automatically be added to your plugin cache. This enables people to open and print documents without downloading the linked images.

If you wish to add the linked images to your plugin cache, select the 'Refresh Image Cache' link in the plugin window.