Open the Fixups Window

Create a new Fixup

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Give the fixup a name

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Click "Additional search path - Choose" in order to create a variable.

Create the variable

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Enter a useful path, e.g. to your desktop folder, so that you will be able to add a folder name.

Save the fixup

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The new fixup shows up in the fixup list

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If you now execute the new fixup a dialog pops up that lets you modify the search path for fonts

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