The knowledge acquisition bottleneck has become the major impediment to the development and application of effective information systems. To remove this bottleneck, new document processing techniques must be introduced to automatically acquire knowledge from various types of documents. By presenting a survey on the techniques and problems involved this paper aims at serving as a catalyst to stimulate research in automatic knowledge acquisition through document processing. In this study, a document is considered to have two structures: geometric structure and logical structure. These play a key role in the process of the knowledge acquisition, which can be viewed as a process of acquiring the above structures. Extracting the geometric structure from a document refers to document analysis; mapping the geometric structure into logical structure is regarded as document understanding. Both areas will be described in this paper, and the basic concept of document structure and its measurement based on entropy analysis will be introduced. Logical structure and geometric models are proposed. Both top-down and bottom-up approaches and their entropy analyses will be presented. Different techniques will be discussed with practical examples. Mapping methods, such as tree transformation, document formatting knowledge and document format description language, will also be described. © 1994 IEEE