The three solutions we support are Google Drive, DropBox, and OneDrive.
On Android, Xodo integrates all three cloud storage solutions directly in the app. Please see the below guides for instructions:
On Windows, we recommend installing the desktop version of the cloud storage application. This will create a folder on your system that is automatically kept in sync. Files in this folder can then be opened like normal files, and changes will be synced seamlessly. You can also pin this folder in Xodo's File page.