You can not share any files from the asset folder directly.
You need to modify your app to be a file provider and then copy the file from the asset folder to the shared directory, then create a URI to the file in the shared directory, then you can share it:
Edit: FileProvider is included as an internal library now. After investigating several issues with the current FileProvider code that you can find in the forum, I decided to make some improvements and implement it in a class. Starting from Android 7 (API 24) you cannot directly share file uris...