The document discusses PE packers used in malicious software. It provides a refresher on the PE file format and import address tables. It defines what a PE packer is, how they work to hide malicious payloads, and techniques used to detect if a file has been packed, such as small import tables, missing/corrupted string tables, unusually small code size, and non-standard section names. Detection of packers involves manual analysis before using tools to identify the specific packer.