How to Open PDFs in PDF Engineer Instead of Mozilla Firefox on Windows

Set PDF Engineer as the default PDF app in Windows

Install PDF Engineer for Windows first, then set its PDF association:

1. Press Windows + I and open Apps > Default apps.
2. On Windows 11, search for .pdf in the file-type search box and select the current app.
3. Choose PDF Engineer and confirm with Set default or the confirmation button shown.

Alternatively, right-click a saved PDF in File Explorer, select Open with > Choose another app, pick PDF Engineer, and choose Always. On Windows 10, check Always use this app to open .pdf files, then select OK.

For more detail, see the Windows default PDF app guide. Changing the association leaves the contents of your drawings intact.

Microsoft: default app settings

Change Firefox’s action for PDF files

Use Firefox’s file-handling preferences to choose the desktop app.

1. Open the Firefox menu and select Settings.
2. Find Applications under General, or Files and applications under Downloads, depending on your Firefox version. Search Settings for PDF if needed.
3. Find Portable Document Format (PDF) and open its Action menu.
4. Choose Use Windows system default application after setting PDF Engineer as the Windows .pdf default. If PDF Engineer is offered by name, you can choose it directly.

Firefox saves a copy when opening PDFs in an external viewer. You may still see a save prompt depending on your download settings.

Mozilla: choose a preferred PDF viewer

If PDF Engineer is not listed

Choose Use other… in the PDF Action menu and select PDF Engineer if it is available in the application picker. Alternatively, return to Windows, confirm the .pdf association, and use Firefox’s system-default action.

If you prefer to choose for each document, select Always ask. To save documents for later review, select Save File and open them from File Explorer.

Mozilla: file types and download actions

Open a PDF that is already in Firefox

For a drawing already in a browser tab, save it using the PDF toolbar’s download or save button. Find the copy in your Downloads folder, then open it in PDF Engineer.

This is useful for a one-off review when you want to leave Firefox’s usual preview behavior in place. Saving and opening one document does not necessarily change the PDF action for future links.

Test a direct PDF link and troubleshoot exceptions

After changing the action, click a new direct PDF link and check that the saved drawing opens in PDF Engineer. Also double-click a local PDF to verify the Windows default independently.

If only one website behaves differently, try its Download or Export PDF command. Firefox’s download actions do not replace viewers embedded in a web page, and incorrect server content types can affect which action is used. If a company setting prevents changes, ask IT to review the PDF action.

Mozilla: download action behavior