I have attached a PDF file to an item using the K2 'attachments' tab. A link to the file shows up nicely on the page as expected, and the file can be downloaded, as expected.
Unfortunately when the file is downloaded, and I try to open it with Adobe Reader, it says:
"There was an error opening this document. The file is damaged and could not be repaired."
I have downloaded the same file from the server by FTP and it opens fine.
Is there something that K2 does that corrupts the file when it is downloaded? Is there are simple fix?

i have dl many pdf files from different places and gotten my fair share of corrupt pdf files
test by zipping the pdf, dl, unzip, and test the file...

Thanks Bill,
The problem was in the creation of the PDF, not it K2.
The solution was to create the PDF in a version compatible with the latest Acrobat (Reader).
This may help others.

I am having the same problem with all my attachments - not just pdf's.

I can open the file fine in the K2 media manager and download it direct from there no problem but as soon as I try to download it from either the site or the item-attachment tab it says the file is damaged and cannot be repaired.

joomla version 2.5.1 k2 version 2.5.4

My solution to the PDF corruption problem was NOT a solution.
Still having this problem with corrupt PDF files being downloaded (have not tried other file types).
When K2store emails the same file, all is fine, however, when downloading the same file using the attachment file in K2, it is corrupt and won't open in Reader.
Anyone else have this problem? I don't think it is the PDF, but rather how it is downloaded.
Are there any other extensions that allow file download from within K2 that work?