When calling a web service that returns data, is the data that's being returned over HTTP limited to binary data?

When calling a web service that returns data, is the data that's being
returned over HTTP limited to binary data?

Meaning, if I have a web service (a WebAPI) that accesses a file share,
picks up a file to return back to the client over HTTP (this file is a
50mb .tpk mapping file), is the data that the calling client receives
limited to binary data (meaning, the client will have to encode the binary
data back to the .tpk file extension in order to use it)? Or can the data
that's returned to the client retain the .tpk file extension so conversion
wouldn't be necessary? Forgive my slight ignorance on this, this is new to
me.