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You will also need to make sure that you're using oXygen version 21 or later (version 20 and 19 might work, as well, but only 21 and greater have been tested). If you haven't yet upgraded, you will need to contact a representative from LIT to get a new license. If you have any issues getting anything set up, just contact YAMS.
Select Options --> Preferences... --> XML --> PDF Output --> FO Processors
Make sure that "Use built-in Apache FOP" is selected. Note, you can also change the amount of memory available to your built-in FOP. In the screenshot below, I've changed the memory to "2000", which allows 2 GB of memory to be used during the transformation process.
In the "Configuration File" section, use the directory icon to select the location on your computer where you saved the fop-preview.xconf file.
Download the EAD file from ArchivesSpace, but make sure to select the "EAD3 Schema" option.
Open the file that you just downloaded (usually in your Downloads directory) in oXygen
With the aspace-plus-excel-at-Yale-v2020-11-15.xpr oXygen project file open, select "6 ArchivesSpace EAD3 to PDF (preview unpublished)" and transform the file.
If you get an error, email Mark Custer and let him know the Resource record that caused the error.