This appears to be a regular archive marked with the PK signature, which you can extract easily. However, the internal files are rather scattered, and models as well as textures should be stored inside.

NJR.zip

We've made new progress. The textures seem to be DDS, PNG, TGA and other similar formats. I spotted multiple signature markers and sorted the textures by their respective address ranges.

The PRM file acts as a large container holding multiple model files. Its exact structure remains unknown, though the model data itself is simple to locate. The layout of model content is rather messy: face indices are sometimes separated from vertex data by large chunks of unknown bytes, while at other times the two are stored consecutively.

Judging by this arrangement, these are likely short-type normal vectors. What puzzles me is the bone IDs corresponding to vertices. Following the structural rules above, bone IDs should appear alongside UVs, normals and weight data within the vertex coordinate block. A vertex is usually influenced by four bones, yet oddly enough, there are only three weight values here.