Agreed, this looks like Volutella Blight, a very common fungal pathogen that can damage Pachysandra. The linked page provides more information. Suppression of the disease essentially entails mowing-down all Pachysandra growth in the affected area, raking-out debris to improve air circulation (and to remove spore-laden material), and letting the patch regrow at its own pace. Be sure to monitor the area closely for watering needs, since the current drought is stressing and hampering growth on many plants, and if Pachysandra is growing under a tree, the root competition will be substantial for what little moisture is present.

Miri

I removed the Pachysandra with the fungus and raked out the debris in the affected area.  Question:  should I spray a fungicide on the unaffected Pachysandra?  If yes, what do you recommend I spray, and should I wait until this extreme heat lessens before spraying?

We don't recommend using a fungicide in this situation. In part, as you noted, nothing should be sprayed during the heat wave (avoid applying any pesticide in temps above 85 degrees). Fungicides are preventative measures, protecting new growth, but they can still fail to work well based on various conditions and won't be able to cure existing disease. They also may risk harm to pollinators or other organisms, and even though the Pachysandra isn't blooming this time of year, drift from a spray might affect other flowers if they are growing nearby.

Multiple reapplications would probably be needed to maintain protection of uninfected foliage, which might be impractical or costly to attempt, but it's up to you. If you opt to try a fungicide, find a product whose label includes Volutella and has instructions for applications to home landscapes (that is, the product usage is not limited to nurseries, golf courses, and other sites that are not residential), and follow all label directions carefully.

Miri