There are a few operations in LiveCycle ES2 that are single-threaded due to various dependencies and limitations.
1) Native2PDF for Microsoft Excel
Conversion of Excel spreadsheets to PDF using Microsoft Excel 2007
2) Native2PDF for Microsoft XPS
Conversion of Microsoft XPS documents to PDF
3) OCRing of PDFs
Converting PDFs containing bitmapped images to searchable text using Optical Character Recognition (OCR)
4) Optimize PDF
Optmizing PDFs to reduce file size, enable Web View etc.