The Choose File interface is very similar to the Choose Image interface and works just like it.
Files can be uploaded directly from your computer using the select files method or using drag and drop into the upload area.
Connect to your Facebook account to draw a file from your Facebook account.
Connect to your Google Drive account to draw a file from your Google Drive.
Connect to your Dropbox account to draw a file from your Dropbox account.
You can link to a file online.