During downloading, Portable Offline Browser can create files with .primary extension and descr.wd3 files.

The purpose of .primary files is to help when updating a loaded Web site. When Portable Offline Browser is told not to load unmodified files, it will check every file to see if it has changed since the last download. If not, the file is not loaded. If it is an HTML file, Portable Offline Browser should have its original copy with unchanged HTML links to follow. The .primary files are the original and unmodified HTML files.

Primary files are also used when existing files are not loaded. To follow links Portable Offline Browser parses .primary HTML files.

Note: .primary files do not increase the traffic. Portable Offline Browser loads only normal files, with .primary files created later.

Portable Offline Browser versions starting from 2.0 do not create .primary files unless you add the following line to the Project's URLs field:

Additional=KeepPrimary

Descr.wd3 files reside in each directory Portable Offline Browser creates and contain information regarding all downloaded files in the directory:

- file name

- original file URL

- date of the last modification on Web server (to check for updates)

- file MIME type as it was returned by Web server (this is useful for offline browsing)

- a sign, if a .primary file was created or not.

Although all these files could be deleted, it is not recommended because this may make Web site updates and offline browsing less reliable.