Open PandaBank and Click on the File menu. Select the Backup Digital PandaBank... Option
Enter a name for the PandaBank (wallet) backup and click Save. I use the current date in the name i.e wallet_YYYYMMDD to name my wallet backups then it is easy to find the most recent version. By default the backup is saved in the C:\Users\username\My Documents folder (Libraries\Documents). For added safety copy the file to a usb thumb drive, a cloud storage account or external hard drive.
You should backup your PandaBank every couple of weeks or 40 transactions whichever is sooner.
If for some reason you need to manually backup your wallet.dat, you can do it using file explorer in windows. Open File Explorer for windows you can press the windows key + r then in the run entry type %appdata%\Pandacoin then press enter. for windows the folder should be something like this C:\Users\%username%\AppData\Roaming\Pandacoin
You should backup the wallet.dat file you find there.