A TIMS (Trekkers’ Information Management Systems) card is a necessary trekking permit required for any trekking activity in Nepal. Besides that, you will need area-specific trekking permits at varied costs based on the region.
For example, you will need an ACAP (Annapurna Conservation Area Permit) if you want to do the Annapurna Circuit trek permit and a Sagarmatha National park permit for the EBC trek. You can get the TIMS card and other area-specific permits at the office of the Nepal Tourism Board office in Kathmandu.