The documentation for ByPic is quite extensive and is constantly being updated it is therefore only available on this website. You can copy and use any of the information here freely but a mention would be nice.
If you need a local copy then use HTTP Track, the site is a flat file system so should copy easily but don't forget it will probably be out of date within weeks.
Data Sheets - There may be a more up to date versions on the Microchip website.
MX1 Family Data Sheet - This is the data sheet for the MX1 PIC32 Family.
MX3 Family Data Sheet - This is for the MX3, BV513,BV514,BV523
MX All Sections Data Sheet -This is the data sheet for the PIC32 Family that includes detailed descriptions of the hardware modules on the IC. This applies to all PIC32, it is quite large and goes into great detail.