Run the PURGE and AUDIT commands to remove any background metadata that might interfere with the export.
While not a direct "converter," the command (part of Express Tools) allows you to use a DWG block as a hatch pattern. Pros: Built-in, no extra cost.
Regardless of the tool you use, the quality of your .PAT file depends on your DWG preparation. Follow these steps:
There are dedicated software suites designed specifically for pattern management.
Do you have a specific you're trying to create, or