When you need to convert multiple documents to PDF for distribution (or from one Office format to another) there are a few utilities around. The most workable I found is the UNOCONV utility which is build on top of LibreOffice / OpenOffice. This uses the OpenOffice conversion facilities rather than a simple PDF print driver.

On Ubuntu it can be installed via Software Center or via apt-get from the core repositories.
sudo apt-get install unoconv
Combined with the -exec option of the Unix find command this makes conversion of whole directory structures a breeze.
#find all Word Documents and convert to PDF
find . -name "*.doc*" -exec unoconv -f pdf {} \;
#find all Powerpoint Documents and convert to PDF
find . -name "*.ppt*" -exec unoconv -f pdf {} \;
To show all the possible conversion formats you can use:
unoconv --show
The following list of document formats are currently available:

bib – BibTeX [.bib]
doc – Microsoft Word 97/2000/XP [.doc]
doc6 – Microsoft Word 6.0 [.doc]
doc95 – Microsoft Word 95 [.doc]
docbook – DocBook [.xml]
html – HTML Document (OpenOffice.org Writer) [.html]
odt – ODF Text Document [.odt]
ott – Open Document Text [.ott]
ooxml – Microsoft Office Open XML [.xml]
pdf – Portable Document Format [.pdf]
rtf – Rich Text Format [.rtf]
latex – LaTeX 2e [.ltx]
sdw – StarWriter 5.0 [.sdw]
sdw4 – StarWriter 4.0 [.sdw]
sdw3 – StarWriter 3.0 [.sdw]
stw – Open Office.org 1.0 Text Document Template [.stw]
sxw – Open Office.org 1.0 Text Document [.sxw]
text – Text Encoded [.txt]
mediawiki – MediaWiki [.txt]
txt – Text [.txt]
uot – Unified Office Format text [.uot]
vor – StarWriter 5.0 Template [.vor]
vor4 – StarWriter 4.0 Template [.vor]
vor3 – StarWriter 3.0 Template [.vor]
xhtml – XHTML Document [.html]

The following list of graphics formats are currently available:

bmp – Windows Bitmap [.bmp]
emf – Enhanced Metafile [.emf]
eps – Encapsulated PostScript [.eps]
gif – Graphics Interchange Format [.gif]
html – HTML Document (OpenOffice.org Draw) [.html]
jpg – Joint Photographic Experts Group [.jpg]
met – OS/2 Metafile [.met]
odd – OpenDocument Drawing [.odd]
otg – OpenDocument Drawing Template [.otg]
pbm – Portable Bitmap [.pbm]
pct – Mac Pict [.pct]
pdf – Portable Document Format [.pdf]
pgm – Portable Graymap [.pgm]
png – Portable Network Graphic [.png]
ppm – Portable Pixelmap [.ppm]
ras – Sun Raster Image [.ras]
std – OpenOffice.org 1.0 Drawing Template [.std]
svg – Scalable Vector Graphics [.svg]
svm – StarView Metafile [.svm]
swf – Macromedia Flash (SWF) [.swf]
sxd – OpenOffice.org 1.0 Drawing [.sxd]
sxd3 – StarDraw 3.0 [.sxd]
sxd5 – StarDraw 5.0 [.sxd]
tiff – Tagged Image File Format [.tiff]
vor – StarDraw 5.0 Template [.vor]
vor3 – StarDraw 3.0 Template [.vor]
wmf – Windows Metafile [.wmf]
xhtml – XHTML [.xhtml]
xpm – X PixMap [.xpm]

The following list of presentation formats are currently available:

bmp – Windows Bitmap [.bmp]
emf – Enhanced Metafile [.emf]
eps – Encapsulated PostScript [.eps]
gif – Graphics Interchange Format [.gif]
html – HTML Document (OpenOffice.org Impress) [.html]
jpg – Joint Photographic Experts Group [.jpg]
met – OS/2 Metafile [.met]
odg – ODF Drawing (Impress) [.odg]
odp – ODF Presentation [.odp]
otp – ODF Presentation Template [.otp]
pbm – Portable Bitmap [.pbm]
pct – Mac Pict [.pct]
pdf – Portable Document Format [.pdf]
pgm – Portable Graymap [.pgm]
png – Portable Network Graphic [.png]
pot – Microsoft PowerPoint 97/2000/XP Template [.pot]
ppm – Portable Pixelmap [.ppm]
ppt – Microsoft PowerPoint 97/2000/XP [.ppt]
pwp – PlaceWare [.pwp]
ras – Sun Raster Image [.ras]
sda – StarDraw 5.0 (OpenOffice.org Impress) [.sda]
sdd – StarImpress 5.0 [.sdd]
sdd3 – StarDraw 3.0 (OpenOffice.org Impress) [.sdd]
sdd4 – StarImpress 4.0 [.sdd]
sxd – OpenOffice.org 1.0 Drawing (OpenOffice.org Impress) [.sxd]
sti – OpenOffice.org 1.0 Presentation Template [.sti]
svg – Scalable Vector Graphics [.svg]
svm – StarView Metafile [.svm]
swf – Macromedia Flash (SWF) [.swf]
sxi – OpenOffice.org 1.0 Presentation [.sxi]
tiff – Tagged Image File Format [.tiff]
uop – Unified Office Format presentation [.uop]
vor – StarImpress 5.0 Template [.vor]
vor3 – StarDraw 3.0 Template (OpenOffice.org Impress) [.vor]
vor4 – StarImpress 4.0 Template [.vor]
vor5 – StarDraw 5.0 Template (OpenOffice.org Impress) [.vor]
wmf – Windows Metafile [.wmf]
xhtml – XHTML [.xml]
xpm – X PixMap [.xpm]

The following list of spreadsheet formats are currently available:

csv – Text CSV [.csv]
dbf – dBASE [.dbf]
dif – Data Interchange Format [.dif]
html – HTML Document (OpenOffice.org Calc) [.html]
ods – ODF Spreadsheet [.ods]
ooxml – Microsoft Excel 2003 XML [.xml]
ots – ODF Spreadsheet Template [.ots]
pdf – Portable Document Format [.pdf]
sdc – StarCalc 5.0 [.sdc]
sdc4 – StarCalc 4.0 [.sdc]
sdc3 – StarCalc 3.0 [.sdc]
slk – SYLK [.slk]
stc – OpenOffice.org 1.0 Spreadsheet Template [.stc]
sxc – OpenOffice.org 1.0 Spreadsheet [.sxc]
uos – Unified Office Format spreadsheet [.uos]
vor3 – StarCalc 3.0 Template [.vor]
vor4 – StarCalc 4.0 Template [.vor]
vor – StarCalc 5.0 Template [.vor]
xhtml – XHTML [.xhtml]
xls – Microsoft Excel 97/2000/XP [.xls]
xls5 – Microsoft Excel 5.0 [.xls]
xls95 – Microsoft Excel 95 [.xls]
xlt – Microsoft Excel 97/2000/XP Template [.xlt]
xlt5 – Microsoft Excel 5.0 Template [.xlt]
xlt95 – Microsoft Excel 95 Template [.xlt]