zTXT files are Palm files so they will have a .pdb extension. They are like PalmDOC files (simple text) except that they use zip compression (zLIB) which is much better than the original PalmDOC compression. Bookmarks in the style of PalmDoc are supported. Annotations of up to 4K per annotation are also supported by this format.
There are ready made zTXT files available in some eBook Stores.
 Database format
The zTXT format is relatively straightforward. The simplest zTXT contains a Palm database header, followed by zTXT record #0, followed by the compressed data. The compressed data can be in one of two formats: one long data stream, or split into chunks for random access. If there are any bookmarks, they occupy the record immediately after the compressed data. If there are any annotations, the annotation index occupies the record immediately after the bookmarks with each annotation in the index having a record immediately after the annotation index.
There are two compression modes for zTXT data.
- Mode 1 divides the source text into 8K blocks and then compresses each block separately. This allows random access by the reader. requires version 1.44 or later.
- Mode 2 compresses the whole source text and then stores it in 8K blocks. This requires decompressing the entire file at once. This is the older mode and has been destandarized and should not be used any longer.
See also the related format zText.