Applications running on rollApp can only access files in cloud storage like Dropbox, Google Drive, OneDrive or Box. Many of these cloud storage systems support automatic sync between your computer and the cloud. This makes it much easier to make changes to a file locally and then continue working on in it in the cloud on rollApp.
You can also use rollMyFile to open files from your local disk by simply dragging then onto a webpage Changes will still have to be saved to cloud storage though.
In addition to that you can use feature called LocalSync to upload a file from your computer to the application already running on rollApp. To that click the “Upload file” button in the rollApp toolbar in running application and select a file to upload. Then click File/Open and select the file you just uploaded in the folders LocalSync. Check out this guide on using LocalSync.