Currently only .jpg and .png image files can be browsed and displayed as kneeboards.
Just copy the files of your kneeboards to a folder on the same drive as your DCS_MovingMap.exe and navigate there using the apps kneeboard browser.
Hint: If you place the images in a folder called '/Kneeboards', MovingMap will automatically show only the files in this folder.
Place your kneeboard files in any accessible folder on your device (e.g. 'downloads' or create one called 'kneeboards') and navigate there using the apps kneeboard browser.
Note: depending on your device, you may have to grant permission to access the file system. On my Android device this was found under Settings > Apps > DCS MovingMap > Permissions > Storage.