Pasdoc can use aspell to check the spelling of your descriptions. Just run pasdoc with the CommandLine option --aspell=LANGUAGE where LANGUAGE is the aspell code of the language that you use in documentation (e.g. en for English; see aspell manual).
Then pasdoc will
Write all the words that you mispelled to standard output, using warnings like
Warning[2]: Word mispelled "foo"
In addition, in your generated documentation all your mispelled words will be displayed in some special way and you will be able to see suggestions for them. E.g. in HtmlOutput each mispelled word will be displayed using some special color, and when you move your mouse over this word, you will see a hint like "suggestions: ...".
For now it's not done in LatexOutput, see ToDoSpellChecking.
You can also use the CommandLine option --spell-check-ignore-words=IGNORE-WORDS-FILE-NAME where IGNORE-WORDS-FILE-NAME is a file that contains words (one word per line) that should be ignored (i.e. not checked).
Prerequisites: Spell checking works on all platforms. aspell must be installed and available in the search $PATH. Windows users can install aspell as part of cygwin, there is also a native Win32 version.
See also: ToDoSpellChecking.