Hi Gundam :-)
You do not tell us the version of Windows they are using, so I will have to
guess at a suggestion. Try the following and see if it helps:
E browser software defaults Acrobat Reader to "OFF" to display PDF files.
You can restore the setting to"ON" by finding an Acrobat document and then
opening it.
Then click Edit> Preferences> Internet> check the box next to "Display PDF
in browser"
If still no joy, try the information here:
http://windowsxp.mvps.org/ie/pdf.htm
http://www.colba.net/~hlebo49/files.htm
or....
Register pdf.ocx files:
Troubleshooting problems opening PDF files in Internet Explorer window:
http://windowsxp.mvps.org/ie/pdf.htm
also..
How to set a default file viewer for pictures, .pdf documents, etc
The path to Folder Options may vary according to your operating
system. It may be:
Explorer-View-Folder Options
Explorer-Tools-Folder Options
Start-Settings-Folder Options
Start-Settings-Control Panel-Folder options.
Installing the Adobe Reader should set it as the default for .pdf
Hope this helps.
Jan

MS MVP - IE [DTS/AumHa]
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> our company using Mdaemon as our email server, when a user login to her
> email
> account through IE, she get some email attachments and is in PDF format,
> when
> she click on the attachment link, a windows pop up and ask her what to do:
> open, save or cancel, when she click open, a windows appear and said that
> cannot open this file, because it cannot find the path: C:\Documents and
> settings\User\local setting\Temporary internet file\Content.IE5\abc.pdf
>
> only this user have this problem, please help me to solve this problem!!
> Thanks very much!!!!!