Osmfilter not recognising .osm file

hi, I converted a .pbf file to a .osm file using osmconvert, however when I go to use osmfilter it does not recognise the file. I know the file works because I have opened it in JOSM and it functions perfectly.

Below is the error and command: ./osmfilter DC.osm --keep="highway=primary =secondary waterway=river natural=peak place=city =town boundary=national_park =adminstrative border_type=state admin_level=4 amenity=university" >DC-sorted.osm osmfilter Error: unknown file format: DC.osm