The TOPAS User Guide is now hosted in a hyperlinked rich text format by ReadTheDocs:
http://topas.readthedocs.org

They also host a PDF version:

The guide for the previous release, Topas 3.0.p1, can be found here

For archival purposes, previous versions of the user guide are available below, but please use the above ReadTheDocs version as it is the most correct an up-to-date:
SelectionFile type iconFile nameDescriptionSizeRevisionTimeUser
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  3943k v. 1 Aug 10, 2016, 6:31 PM Joseph Perl
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  3963k v. 1 Aug 10, 2016, 6:31 PM Joseph Perl
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  3992k v. 1 May 27, 2016, 10:51 PM Joseph Perl