The Save As PDF command in MS Office 2007 allows you to create a PDF from a Microsoft Office document even if you haven’t got Adobe Acrobat installed. However, if the Office document contains images, the image in the PDF document will have "alt text" attached to it.

The purpose of alt text (short for alternative text) is to provide a textual description of the image. This description will be displayed as a tooltip when a user hovers their mouse over the image. The description will also be "heard" by anyone using screen reading software.

By default, the filename is used for the alt text. If the filename is either meaningless (for example1.jpg) or not overly-descriptive, it is recommended that the alt text is amended.

I've written a short tutorial that explains how to amend (or remove) the alt text from Word 2007 images: http://mthomas.co.uk/word-2007-images-amending-alternative-text