"set terminal pdf" produces no output

Binary package hint: gnuplot

Following gnuplot source generates no output when run as "gnuplot file.plot":
---
set terminal pdf enhanced

f_c(x) = x**2
f_d(x) = floor(x)**2

plot f_c(x) linetype rgb "red" title "Continuous", \
  f_d(x) linetype rgb "blue" title "Discrete"
---

Changing the terminal to "png" outputs a regular png file though.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: gnuplot (not installed)
ProcVersionSignature: Ubuntu 2.6.35-23.37-generic 2.6.35.7
Uname: Linux 2.6.35-23-generic i686
Architecture: i386
Date: Tue Nov 16 15:33:25 2010
InstallationMedia: Kubuntu-Netbook 10.04 "Lucid Lynx" - Beta i386 (20100318)
ProcEnviron:
 LANGUAGE=en_GB
 PATH=(custom, user)
 LANG=en_GB.utf-8
 SHELL=/bin/bash
SourcePackage: gnuplot
---
Architecture: i386
DistroRelease: Ubuntu 10.10
InstallationMedia: Kubuntu-Netbook 10.04 "Lucid Lynx" - Beta i386 (20100318)
Package: gnuplot-nox 4.4.0-1 [modified: usr/bin/gnuplot]
PackageArchitecture: i386
ProcEnviron:
 LANGUAGE=en_GB
 PATH=(custom, user)
 LANG=en_GB.utf-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.35-23.37-generic 2.6.35.7
Tags: maverick
Uname: Linux 2.6.35-23-generic i686
UserGroups: adm admin cdrom dialout lpadmin netdev plugdev sambashare