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Summary: Microsoft Outlook makes it easy to manage emails. But it can be incredibly frustrating when you attempt to open an attachment and it opens in the wrong application. When this happens, you might find that PDF files are opening in a web browser instead of Adobe Acrobat. This is when knowing how to set a default app becomes very valuable.

In this blog, we will cover why attachments would open in the wrong program and how to change default program to open attachments in Outlook. We will also discuss applicable limitations along with manual methods to make your Outlook experience more convenient.

Also Read: Save Attachments From Multiple Emails in Outlook

Why Attachments Open in the Wrong Program in Outlook?

Outlook does not have a dedicated setting for the choice of opening attachments. But it uses the settings for file association in Windows. Unless you specify a certain program to open .pdf, .jpg, .docx, etc. Windows will pick the default you have set, usually not your preferred setting. 

Here are a few common reasons for unwanted default applications:

• The file associations were never customized.

• You may have had a new app that changed your default settings. 

• Installed updates for Windows or an application may have undone your file associations. 

• Corrupt registry entries may affect the default program's file behavior. 

• Outlook was set up as a new computer and your preferences were not imported.

Manual Methods to Change Default Program for Outlook Attachments

Because Outlook uses Windows default file associations, the only way to change this is how Windows manages the particular file type you are having a problem with.

Method 1. Use "Open With" in Windows

This feature comes within Windows and you can have it on your respective PC.

• Find an attachment file on your desired computer.

• Right click on the file and select Open with > Choose another app.

• Choose the program you want to use.

• Click the box that says "Always use this app to open .[type of file] extension".
  Click OK.

This change will now apply when you are opening the same attachments in Outlook.

Method 2. Change File Associations Through Windows Settings

The second method is to use your Windows settings to change the default program to open attachments in Outlook. Here are these few steps which you need to follow.

1. Press Windows + I to open Settings.

2. Select Apps > Default apps.

3. Scroll down and select Choose default apps by file type.

4. Go through and find the file extension (i.e. .pdf, .docx, .xlsx).

5. Click the default app and choose the desired app from the list.

Note: You could also choose default apps by protocol or even set the default defaults for one particular application.

Method 3. Use Control Panel to Change

Another method to change your default program to open attachments in Outlook. It has quite a few steps involved in it.

• Open the Control Panel first.

• Click Default Programs > Associate a file type or protocol with a program.

• Scroll through the list to locate the file type you want to change.

• Click on the change program and select the application you want to use.

Be Careful About its Limitations

Changing default file associations can resolve the problem for many users, but there are drawbacks too:

• Outlook does not support changing default programs within the program.

• You have to change each file type individually.

• Some enterprise IT policies have restrictions for changing defaults to apps.

• If the file extension is not properly registered, it may not show up in Windows.

• The changes made on one device will not sync to another one unless you are using roaming profiles.

Change Default Program to Open Attachments in Outlook - Expert Solution

Let's say you receive a lot of attachments in Outlook such as PDFs, Word documents, images, spreadsheets, etc. And let's say you store all attachments in specific applications. Opening each Outlook attachment one at a time can take a long time. That's where the SysTools PST Attachment Extractor can help. After the attachments are saved locally, you can open them with the appropriate default app without Outlook opening or using the wrong program.

Key Benefits:

• Extracts attachments from multiple PST, OST, or BAK files.

• Keeps folder structure.

• Allows filters by file type, size, and date.

• Helps reduce storage by detaching large attachments from mailboxes.

Conclusion

To change the default program for opening attachments in Outlook, you are simply changing the file association in Windows. This applies to PDFs, Excel files, images, and more. Once you set the default program for a file type, Outlook will use that program to open attachments of that file type.

Take care of the following points:

• Use "Open with" for quick changes.

• Use Windows Settings or Control Panel for permanent and large scale changes.

• If you are in an enterprise, understand the limitations.

Highly recommend if you are in a bind with a non-accessible OST file and need to convert to PST.