A Custom Format is a workspace that can be used to preprocess data as if it were a data format on its own. Once created, it will show up in the reader formats list. From then on, it can be used in any FME component as a separate format, including application extensions.
Note A Custom Format can only be a reader.
When you create a Custom Format, you can, in effect, define your readers, your workflow, and the format's schema, and you can use it like a standard Source Format. This is useful if you consistently use the same information in a translation, and when you consistently perform the same processing on datasets.
After you create and save the format, it will be selectable from the Reader Gallery.