Use the DXFOUT command and save the file as a to ensure maximum compatibility.
To create a true, portable .pat file from raw line geometry, specialized software or plugins like HGEN (Hatch Pattern Generator) are required. SAVING AUTOCAD DWG AS .PAT FILE - Forums, Autodesk
Standard PAT files do not support true arcs or circles . Only straight line segments. Fix: In your DWG, replace arcs with a polyline using PEDIT and the "Decurve" option. Then approximate the curve with short line segments (this increases file size).