Does anyone know how to generate document thumbnails in Ruby (or C, python...)
Not sure about .doc support in any open source library but ImageMagick (and the RMagick gem) can be compiled with pdf support (I think it's on by default)
As the 2 previous posters said, ImageMagick's probably the easiest way to generate the thumbnails.
You could exec something like:
´convert -size 300x300 doc.pdf doc.png´
(The backquotes tell Ruby to shell it out).
If you don't want to use exec to do the conversion you could use the RMagick gem to do it for you but it's probably a bit more of code.
A simple RMagick example to convert a PDF to a PNG would be:
require 'RMagick'
pdf = Magick::ImageList.new("doc.pdf")
thumb = pdf.scale(300, 300)
thumb.write "doc.png"
To convert a MS Word document, it won't be as easy. Your best option may be to first convert it to a PDF before generating the thumbnail. Your options for generating the PDF depend heavily on the OS you're running on. One might be to use OpenOffice and the Python Open Document Converter. There are also online conversion services you could try, including http://Zamzar.com.