Note: In order to edit files stored on Jottacloud with Office, there are some requirements:
You must have an office 365 subscription
Your device must be running Android KitKat (4.4) or above
Assuming both conditions are met, the rest is simple.
To open a file in Office
Click "Open" from the home screen (in the bottom-right corner) and then select Browse (the bottom-most menu option)
Android's native file browser will open. To navigate to your Jottacloud folders, click the hamburger icon in the top-left corner. A navigation drawer will open. Below the local storage options, you will see a list of all of the Document Providers registered on your device. Among them you should find Jottacloud (note: if Jottacloud does not appear, see below about troubleshooting)
Click on the Jottacloud option to see an overview of the four storage categories in Jottacloud: Synced, Backed up, Archive, Shared. From the storage categories you will be able to navigate your Jottacloud-stored files as you would from the app; the Jottacloud directory structure is retained in the Androids file browser. Navigate to the document you want to edit (note: invalid items are still displayed in the file picker, but are faded)
Click on the document to load it
Office will load the document, and from there you are free to edit the file without hassle. If you have autosave enabled in your Office app, the file will automatically save and update when you are finished editing.
You also have the option to "Save As", which will prompt you to fill in a filename and select a save location, where you will be presented with the same location options that you were given when first opening the file for editing.
If Jottacloud does not show up as a location in Android's file picker, you can try the following:
Check to be sure that your Jottacloud app is logged in
Try closing and reopening the Jottacloud app to force it to re-notify Android of its status as a document provider
Double check that you have met the requirements outlined above for editing files with Office
Let us know you are having trouble and we'll help you solve it
If you can only open files in read-only mode:
Be aware that you can only edit documents from within the Office app. If you are in the Jottacloud app and are trying to open the document from our native file browser, you will only be able to view it in read-only mode
Check that your Office app is signed in to an active Office 365 account