While pdf file can't be displayed in IE

The customers have updated their computers and then they found pdf can't be displayed by IE6 from our web system. When clicked the button in a webpage, an ie window with pdf file content in it would be opened before updating. And now the opened window will be closed as quickly as it opened. I googled it for a long time and finally found the solutions. First, in the internet option there is an advanced setting which prevents saving content from encrypted page. You can find it in the Advanced tab as 'Do not save encrypted page to disk' at Security group. The customers connected our web system using https and they checked this option, so pdf file is prevented to save on the disk after IE downloaded it and therefore acrobat can't open the pdf file. Uncheck this option is the first step for the solution. Second, try to open pdf again, and if it still can't be displayed, check the settings of your security. In the internet option click the 'Security' tab and click the 'customize level' button. This will open 'Security Settings' window. In this window you can find the setting of 'show dialog automatically when downloading files' at the 'Download' group. Enable this option and then a warning dialog will be displayed when you attempt to open a pdf file. Uncheck the option 'Always warn while trying to open a file of this type' before click the 'Open' button on the warning dialog. OK, now pdf file will be displayed in IE automatically without a warning dialog being displayed. By the way, if you want to restore the warning dialog, just delete the key from registry under 'HKEY_CURRENT_USER\Software\Microsoft\Windows\Shell\AttachmentExecute\{0002DF01-0000-0000-C000-000000000046}' which name is 'AcroPdf.Pdf.1'.