The XDC file should be added to every Vivado project.
If you are thinking of the board files, these can be added to the Vivado installation (once), and will be available for every project. PYNQ-Z2 board files are here:
https://d2m32eurp10079.cloudfront.net/Download/pynq-z2.zip
(Add to Vivado install path]\Xilinx\Vivado\20XX.X\data\boards\board_files )
Cathal