By design, ABBYY FineReader 15 and 14 can use N-1 cores from N cores available for the processor.

This leads to N-1 Background executor processes (FineExec.exe) being started after the user launches ABBYY FineReader.
Example: If the computer has N= 8 CPUs then N-1= 7 FineExec.exe processes will be launched.

You can change the default settings in ABBYY FineReader > Tools > Options > Other > Number of processor cores to use for OCR.