I'm assisting a mate with this problem. I have a similar XP system with Pegasus mail and don't have this problem and I've compared many settings between the 2. 

The raw attachment header contains -

--=_alternative 0079438A4A2576B8_=--
--=_mixed 0079438A4A2576B8_=
Content-Type: application/octet-stream; name="20100128074017800.pdf"
Content-Disposition: attachment; filename="20100128074017800.pdf"
Content-Transfer-Encoding: base64

The sending email client isn't clearly identified in the headers. The particular email is sent through Lotus Notes but PDF documents from other senders have the same problem.

When trying to view an Adobe PDF document as an attachment to a message it gives

the following error -

"Adobe reader *.* has encountered a problem and needs to close."

*.* = 7.0, 8.2 or 9.2

I've also updated Pegasus mail to 4.52 and tried adding the file type pdf and

specifying the acrobat program as the desired program without success. If I save

the pdf file to a folder on the pc then I can manually open the file in acrobat

reader without problems.

I've seen mention of this a couple of times in the pmail forums but no solution

to my problem was found. OS = XPSP3.

This is exactly the same as I'm experiencing -

http://community.pmail.com/forums/post/7421.aspx

[quote user="jebz"]

When trying to view an Adobe PDF document as an attachment to a message it gives

the following error -

"Adobe reader *.* has encountered a problem and needs to close."

*.* = 7.0, 8.2 or 9.2[/quote]

Can you provide the header section of the attachment from the message's raw view? It should look like this one:

------=_Part_77504_5021536.1102268941652
Content-Type: application/octet-stream; name=7E00F3FF.pdf
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=7E00F3FF.pdf

Did Pegasus Mail send it or another email application?