It is part of the binary-to-text encoding used to include graphics or formatted documents within a plain text submission.

Sites like Disclosure Quest archive these raw text files, where the string is visible to anyone searching for specific file extensions within government data. Conclusion

The sequence "4C.7z" is simply a coincidental result of the encoding process. It is not a real 7-Zip file, nor is it a hidden "leaked" archive. Where You’ll Find It