The "paper" you are likely looking for refers to the or the RAR password required to extract the files.

For files from that specific source, the password is almost always: Quick Tips for Extraction: Case Sensitivity: Make sure to type it in all lowercase.

Ensure you have all parts (part1, part2, etc.) in the same folder before you start the extraction of part1.

Use a modern extraction tool like 7-Zip or WinRAR to avoid "Header Corrupt" errors.