Currently, you are permitted to upload the following file types to your WordPress.com blog (no upgrade required):
See the Images help page for examples and details.
.pdf (Portable Document Format; Adobe Acrobat)
.doc, .docx (Microsoft Word Document)
.ppt, .pptx, .pps, .ppsx (Microsoft PowerPoint Presentation)
.odt (OpenDocument Text Document)
.xls, .xlsx (Microsoft Excel Document)
See the Uploading Documents help page for examples and details.
With the purchase of a Space Upgrade you are also permitted to upload zip files and the following audio file types, in addition to the basic file types listed above:
There is an embedded audio player built in to WordPress.com that will work with .mp3 files.
With the purchase of the VideoPress you are permitted to upload the following video file types, in addition to the basic file types listed above. Note that purchasing VideoPress will not enable you to also upload audio files. If you wish to upload audio files, you need the Space Upgrade, as well.
.mp4, .m4v (MPEG-4)
.wmv (Windows Media Video)
Before uploading files to your blog, please ensure that you own, or have the legal right to distribute, them. If you do not own the files, and do not have express permission from the owner or copyright holder, you may NOT place them on your blog.