curl -X PUT https://api.box.com/2.0/files/12345/watermark \
     -H 'Authorization: Bearer <ACCESS_TOKEN>" '
     -H 'Content-Type: application/json" '
     -d '{
       "watermark": {
         "imprint": "default"
       }
     }'

BoxWatermark watermark = await client.FilesManager.ApplyWatermarkAsync("11111");

BoxFile file = new BoxFile(api, id);
file.applyWatermark();

watermark = client.file(file_id='12345').apply_watermark()
print('Watermark created at {0} and modified at {1}'.format(watermark.created_at, watermark.modified_at))

client.files.applyWatermark('11111')
	.then(watermark => {
		/* watermark -> {
			watermark: 
			{ created_at: '2016-10-31T15:33:33-07:00',
				modified_at: '2016-10-31T15:33:33-07:00' } }
		*/
	});