Although its likely, that some file extensions may be missing from the list of associated file extensions with the application, yet they can be opened, be part of, or otherwise be associated with the program. LibreOffice default file extension associations The most common file.

If you had Microsoft Office installed prior to installing OpenOffice.org (OOo):

• OOo v3.0.0 - OOo will not become the default application for MS file types. It does not provide an option during install for an option to affect this behaviour. The lack of option here is assumed to be a bug and possibly this will be fixed in new releases.
  
• OOo v2.4.2 and previous versions - OOo will give the user an option during install on whether to make this the default program for MS Office file types or not.

Regardless of what options you took during installation, or your current configuration, it is an easy task to make either OOo or MS Office the default application for a particular file type.
Windows XP
Different ways to do this:
1) The easiest method is to simply right click on a file that you want to open. Select 'Open With..', then 'Choose Program..'.
From the dialog box that pops up select the program you want to make the default application (if it was a doc file then select swriter if you want Open Office to handle these files or Microsoft Word if you prefer that). You should be able to find it, but if you can't you can press 'Browse' and search for the program's main executable file.
Select 'Always use the selected program to open this kind of file', and press OK. Now this program is the default. You can repeat this process for various file types (e.g. doc, xls etc.).
2) Or tell Windows what program to use to open what type of files:
This application has been reported to be successful in this forum.
Running this utility should set the associations correctly: OOoAssociation Utility.
3) The other option is to open Windows Explorer and then select:
Tools->Folder Options..->File Types
From here you can find a particular file type such as 'doc', and press 'Change' and you will be presented with the same dialog as in step 1. You can use this list to quickly set the default application for all the relevant file types.
Windows Vista
Methods 1 and 2 for Windows XP will work for Vista too, but there is also another option. It's not often I have good things to say about Vista, but I am pleased to announce that this is definitely one occasion where it can make life easier.
4) Start button->Control Panel->Programs->Default Programs->Set your default programs
Now find OpenOffice.org or Microsoft Office in the list and after selecting the appropriate one you can either choose 'Set this program as default' to make it the default application for all file types it can handle in one fell swoop, or 'Choose defaults for this program' to quickly pick the file types you would like this program to handle.
If you have a section to add for a different OS please do so.

How to change default programs (file associations) to open attachments in Outlook?

Normally when you open an attachment of CSV file in Outlook, it is opening within Microsoft Excel by default. But now you want to open the attachment of CSV file within Notepad, could you figure it out? In this article I will introduce two solutions to change the default programs (or file associations) to open attachments in Outlook.

Change default programs (file associations) to open Outlook attachments by Open with feature

Change default programs (file associations) to open Outlook attachments in Control Pane

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Change default programs (file associations) to open Outlook attachments by Open with feature

If you can find out the same type of files (the CSV file in my example) in your Computer, please follow below steps to change the default programs or file associations about opening specified type of Outlook attachments.

1. Go to the folder containing the specified type of file, right click this type of file, and select Open with > Choose another app (or Choose default program) from the right-clicking menu. See screenshot:

2. In the opening dialog box, please: (1)Click to select the new program you will open this type of attachments with; (2) Check the Always use this app to open .CSV files option (or Always use the selected program to open this kind of file option); (3) Click the OK button.

3. Now the selected file is opening with the specified program. Please close it without saving.

From now on, all files of the specified type will be opened with the new program by default, including this type of Outlook attachments.

Change default programs (file associations) to open Outlook attachments in Control Pane

You can also associate the specified file type of Outlook attachments to a program in Control Panel to change the default programs of opening specific kind of Outlook attachments.

1. Please open the Default Programs in Control Panel with opening a folder and pasting below path into the address box:
Control PanelAll Control Panel ItemsDefault Programs

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2. Now you get into the Default Programs dialog box, please click the Associate a file type or protocol with a program option. See screenshot:

3. In the Set Associations dialog box, please click to select the extension of the specified file type (.csv in my example), and then click the Change program button. See screenshot:

4. Now in the popping up dialog box, please click to select the new program you will open the specified type of files with, and click the OK button. And finally close the Set Association dialog box. See screenshot above:

From now on, all files of the specified file will be opened with the new program by default, including this type of Outlook attachments.

Demo: change default programs (file associations) to open Outlook attachments

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• BCC Warning - show message when you try to reply all if your mail address is in the BCC list; Remind When Missing Attachments, and more remind features..
• Reply (All) With All Attachments in the mail conversation; Reply Many Emails in seconds; Auto Add Greeting when reply; Add Date into subject..
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