mjhjmtu

I downloaded iftex from CTAN and installed it. I think I'm using it according to the documentation:

documentclassarticle
usepackageiftex
ifPDFTeX
 errmessageDon't use pdflatex. Use plain latex and dvipdf
else
 errmessageGood. You aren't using pdflatex
fi
end

However, this construct does not recognize pdflatex . I get the message "Good. You aren't using pdflatex" whether I use latex or pdflatex.

$ latex iftex.tex
This is pdfeTeX, Version 3.141592-1.21a-2.2 (Web2C 7.5.4)
entering extended mode
(./iftex.tex
LaTeX2e <2003/12/01>
Babel <v3.8d> and hyphenation patterns for american, french, german, ngerman, b
ahasa, basque, bulgarian, catalan, croatian, czech, danish, dutch, esperanto, e
stonian, finnish, greek, icelandic, irish, italian, latin, magyar, norsk, polis
h, portuges, romanian, russian, serbian, slovak, slovene, spanish, swedish, tur
kish, ukrainian, nohyphenation, loaded.
(/usr/share/texmf/tex/latex/base/article.cls
Document Class: article 2004/02/16 v1.4f Standard LaTeX document class
(/usr/share/texmf/tex/latex/base/size10.clo))
(/usr/share/texmf/tex/latex/iftex/iftex.sty)
! Good. You aren't using pdflatex.
l.6 errmessageGood. You aren't using pdflatex

? x
No pages of output.
Transcript written on iftex.log.
$
$ pdflatex iftex.tex
This is pdfeTeX, Version 3.141592-1.21a-2.2 (Web2C 7.5.4)
entering extended mode
(./iftex.tex
LaTeX2e <2003/12/01>
Babel <v3.8d> and hyphenation patterns for american, french, german, ngerman,
[...]
nohyphenation, loaded.
(/usr/share/texmf/tex/latex/base/article.cls
Document Class: article 2004/02/16 v1.4f Standard LaTeX document class
(/usr/share/texmf/tex/latex/base/size10.clo))
(/usr/share/texmf/tex/latex/iftex/iftex.sty)
! Good. You aren't using pdflatex.
l.6 errmessageGood. You aren't using pdflatex

? x
No pages of output.
Transcript written on iftex.log.
$

Am I doing something wrong?

The ifPDFTEX test is checking the engine in use (TeX90 vs pdfTeX vs XeTeX vs LuaTeX), not the output format. For that, you want the ifpdf package

documentclassarticle
usepackageifpdf
ifpdf
 errmessageDon't use pdflatex. Use plain latex and dvipdf
else
 errmessageGood. You aren't using pdflatex
fi
end

In recent TeX Distributions latex is actually a symbolic link (or the equivalent in systems that don't support symbolic links) to pdftex (actually pdfetex) which runs the latex format in dvi mode.