When Fujitsu told us the ScanSnap S500 could scan 18 pages of A4 per minute, and convert them into PDF format at the push of a single button, we just had to try it for ourselves. It's always great fun shattering this type of PR hype, but to save you the trouble of skipping to the end of the review we'll own up now, with suitably red faces, that our review machine whizzed through an average of 19.28 pages per minute. And yes, it does convert into flawless PDF format at the push of a large green button.

The machine is aimed at a very specific market of office workers who frequently need to convert paper documents into electronic files for editing or archiving, but who are not scanning or computing professionals. The ScanSnap therefore needs to be simple to operate and small enough to sit inconspicuously on a desktop when it's not being used, but large enough to handle all standard document and letter sizes.

When folded away the scanner is tiny, even smaller than its picture suggests. The actual dimensions are 28.4cm wide and 15.7 deep, which is way smaller than a sheet of A4 paper. Preparing the scanner for action involves swinging up the hinged sheet feeder (capacity 50 pages) and pulling forward a paper output tray.

The sheet feeder handles the standard document sizes of A5, B5, A4, UK Letter and anything in between, and it can accommodate newspaper clippings and irregularly-shaped documents if they are first placed inside a transparent carrier sheet.

The carrier sheet also provides a means of scanning A3 documents if you don't mind folding them. This is possible because the scanner has a duplex facility in which it scans both sides of a page at the same time, so if you fold an A3 page and scan it in duplex mode, the software on the host PC can seamlessly stitch both sides together.

Using duplex mode slightly slows down the scanning process to 15 pages per minute, but as you are actually scanning 30 sides, this can be forgiven. The additional time required to process a set of scans and turn them into a PDF file depends on the power of the host PC. On our office workhorse machine, which is not very powerful, it took less than two seconds per side.

By default, scanned pages are saved as page images, but you can opt to have them made searchable. Obviously, this involves an OCR phase which adds considerably to the post-processing delay. Blank pages are ignored, so you can freely mix single-sided and double-sided documents, and pages are rotated automatically so you can also mix landscape and portrait documents.

Three items of software are supplied with the scanner. The main item is a full version of Adobe Acrobat 7.0, which handles all the PDF processing; then there's a dedicated version of ABBYY FineReader OCR, which converts scanned documents into editable Microsoft Office files.

Binding these two together is ScanSnap Manager, which intercepts the scans and sends them to the appropriate program for processing. It's also where you can adjust settings and options should you need to. The big decision is scan quality, which can be switched between Normal, Better, Best and Excellent - where Excellent is better than Best (please direct your e-mails of linguistic complaint to Fujitsu, not to us).

Normal mode is the fast one, and it's ideal for black and white text documents. Better mode is slightly slower but with a marginal increase in output quality. In Best mode, throughput drops to 6 pages (12 sides) per minute, but it's great for documents with coloured fonts, shaded backgrounds and photographs. Forget Excellent mode: you don't need it.

In reality, mode selection is just a way of hiding the intricacies of optical resolution from the user, and the four modes correspond to 150, 200, 300 and 600 dots per inch. Neither are users bothered with decisions about paper size and whether to scan in colour or monochrome, both of which are detected automatically.

The ScanSnap S500 is a business tool and not a general-purpose scanner. You can use it to scan photographs, but not with any great measure of control, and its scans can only be saved in PDF and JPEG formats. Neither TWAIN nor ISIS drivers are provided, so you can't use it with ordinary imaging software, and obviously it can't scan anything that won't go through the sheet feeder.

Despite these limitations, for its designated purpose of rapidly and effortlessly turning paper-based office documents into their electronic equivalents it's unbeatable.

If you're thinking of buying Adobe Acrobat and a scanner to convert office documents into electronic formats, don't. Buy ScanSnap instead. Given the value of the bundled software the scanner is virtually free, and it's an absolute joy to use.