Problems with Adobe pdf files as attachments in Mail

Question

I have 4 Adobe pdf files that I can open and view without a problem.
The minute I try to attach them to an email to send to someone else, they show in the email as blank pages with the message that in order to be viewed, a more recent version of Adobe needs to be downloaded. It doesn't make sense - if my Adobe is up to date enough to open them normally, why can't Mail open them as attachments?
Flummoxed!

Answer 1

I have sent you an email reply with the following text:
I would not say things are exactly OK, but here is what I found out:
The two documents were produced by the program described at the link below:
http://www.adobe.com/products/livecycle/designer/
The forms, which would open in Adobe Reader 9, are filled out -- typically forms that you file out on such agency sites are only printable, and cannot be Saved in a filled out form -- yours are filled out with data -- data that could be sensitive. I will delete them very quickly, as soon as we have concluded any discussions.
Neither file could be opened with Adobe Photoshop CS3, except to show the same error message, which is pretty unusual, nor could they be opened with Graphic Converter any differently, which is equally unusual.
The file header, when observed in Raw Source, says the application that produced it is unknown -- a good reason Mail nor Preview could open. I am pasting in one of the file headers from Raw Source view:
--------------090301040801050804080205
Content-Type: application/x-unknown;
name="09.02.06 FKR IT34 Assessment 2008.pdf"
Content-Transfer-Encoding: base64
Content-Disposition: inline;
filename="09.02.06 FKR IT34 Assessment 2008.pdf"
All-in-all I would say these are very unusual files.
Ernie