Although the installer includes a nice HTML manual, if you want a pretty PDF version, check out the Serious Sam Gold Edition (1&2) manual available here:
http://files.seriouszone.com/download.php?fileid=875

[This appears to be a completely legit and well-known site, so I don't think the publisher has any issue with it.]

(And the manual in one form or another is worth glancing through, at least to find the non-configurable keys!)