The simplest container of digital information is the file and among the vast array of files currently available, MS-Office files are the most widely used. The “Microsoft Compound Document File Format” (MCDFF) has often been used to host secret information. The new format created by Microsoft, first used with MS-Office 2007, makes use of a new standard, the “Office Open XML Formats” (OOXML). The benefits include that the new format introduces the OOXML format, which lowers the risk of information leakage, as well as the use of MS-Office files as containers for steganography.This work presents some new methods of embedding information into the OOXML file format which can be extremely useful when using MS-Office documents in steganography. The authors highlight how the new methods introduced in this paper can also be used in many other scenarios, not only in MS-Office documents. An evaluation of the limits of the proposed methods is carried out by comparing them against the tool introduced by Microsoft to sanitize MS-Office files. The methods presented can be combined in order to extend the amount of data to be hidden in a single cover file.