Originally, applications on Palm OS® devices were capable of only accessing data organized in the Palm database format since everything in the memory of a Palm OS® device was a database in that format. As a result the iSilo™ document format had to use that format as the top-level format for its data. Hence, files in iSilo™ format will most likely have an extension of .pdb. Files with an extension of .pdb are generally in the Palm database format. However, please note that even though a file may have an extension of .pdb, chances are that it is not a file that is a document in iSilo™ format unless you are specifically told that it is.
As mentioned earlier, iSilo™ and its document format was originally designed for the Palm OS®. The presumption was that on a desktop computer, a person would have access to the original source of the document. Presumably, the author would make available an HTML version of their document. However, many documents currently available in iSilo™ format were specifically formatted for that format and are not readily available in HTML format by the creators of those documents. So iSilo™ for Windows® fills the need for a desktop version.