We wrote Transformer to assist in the rescue of textual data from obsolete file formats such as DOS word-processor files. Sometimes, it proves impossible to rescue old data through normal means such as running the original application and exporting to a format which can be imported by a more modern program. Perhaps the program which created the data no longer exists or cannot be run on available hardware, or perhaps it cannot save to any format but its own. In these circumstances, it is often necessary to rescue the data by a process of manual conversion, identifying blocks of text or other data in the original file which can be replaced with Unicode characters, and building sequences of replacement operations which gradually convert the data. This often requires an exhaustive trial-and-error approach in which transformation operations are added incrementally and tested in various sequences before a reliable sequence is developed; then the sequence can be run on a group of files. Transformer should provide as efficient a working environment as possible, so that the user can focus on the task itself rather than the machinery.