I've always thought that PDF is quite efficient. Most of the times it's smaller than the MS Word document that was used as the source.

Unfortunately I have not been able to convert a MS Word document to PDF using OO Writer without sacrifying filesize.

Example:
A 48kB word document becomes a 384kB PDF?

1. Is PDF efficient?
2. If so, how can I reduce the size (used 80% quality and 150 DPI)

Not 100% sure if it belongs here or in the software section.

PS The document contained one or two pictures

Try converting the file to open-document format before exporting to pdf.

Portable Document Format is not used for it's efficiency (which will vary according to what is in the document). It is used for portability - it looks the same in any computer.

If bandwidth is an issue - archive it.

Just playing around with OOo's export to pdf feature ... I don't know how it works on word, but OOo gives a whole range of compression options.

Exporting a color file which is mostly image: size - 160.7kB
Using 90% jpeg compression, and keeping image resolution the same (150dpi), reduces file size to 155.5kB - or 97%

Sacrificing data (jpeg compression 75%), and this becomes 104.1kB - or 65%
Sacrificing image resolution (75dpi but still 90% jpeg), this becomes 77.9kB - or 48%

... see what I mean.

I played with the quality (compression) and the DPI and it makes a minor difference (but still bigger than the original).
Also saved as ODT first.

Sorry that I did not mention it explicitely.

I will give it a shot with a clean OOo document (copy/paste or just retype it all).

Main reason to convert is to make it portable for publication on the internet. But bandwidth/speed is an issue in this part of the world as broadband is only now gaining popularity.

And main reason for the question is that most documents get smaller (as you also indicated).

Last time I checked Word didn't even have any export to PDF facilities.

I think Simon means 'on word documents'.

I wouldn't use Word docs for publication, since you can't be sure people have just that version of Word available. It might open in OO.org or other versions of Word (befeore MS takes in use their securing software) but it wouldn't perhaps look quite the same; and those without Word or OO.org might have trouble hunting for the whole suite or small "Word Reader" applications, or paying some money for them. It's easier to use pdf or other similar formats since Adobe Reader (or the lighter, faster readers) are available at no cost, and pros are the documents stay looking like you created them. And if you think about the future, probably the amount of broadbands increase there too, and soon when the filesize doesn't matter if it's only some hundred kilos or less, you are worried about the outlook of the documents.

As said, pdf (or ps) isn't about file size, but about the way it looks and is. Word docs are great if you print them right away or use them only for yourself or use them as the base of a ps or pdf file, but I don't see much sense in using doc format when publishing documents on the web; there are too many differencies between the Word and other Doc reader versions, and more or at least as many users have Adobe Reader or equivalent as have Word or equivalent, I'm pretty sure about that. Another option is to publish the content as images, which are even more commonly readable, but then you'll surely lose in filesize.

Now I'm not sure about the newest Offices (XP and newer), but the older ones didn't have it at least. There is always a possibility of installing a PDF Printer on the system, and use it like you would use a regular printer to produce pdf files. This is also what you can do on Linux. You can even get the "official" Adobe PDF printer, though there are other PDF printers around; they are usually somehow customized for some certain task, like to work for a certain (server) program rather than the user directly.

PDF is not the ideal web format. It is good for general documentation and stuff, but not for online viewing. It's much better for printable documents. (X)HTML is better for online documents. Horses for courses.

Consider creating web-enabled pages in pdf format via pdflatex instead.

pdf documents can be made almost arbitrarily smaller - sacrificing quality (save as 0% jpeg for eg) but the exact saving will depend on the document. There are lots of other ways to save space - leave off all images for eg.

In the end, you'll get better service with html, as mentioned.