What software was used for these schematic diagrams?
The presence of "Corel Office Document" in the properties of one of the PDF documents suggests that Corel Draw was used to produce them.

Electronic symbols libraries are available for Corel Draw.

The presence of "Acrobat Distiller 4.05 for Windows" might mean that Acrobat Distiller was then used to shrink some of the PDFs and/or make them more generally compatible with PDF readers.