Hi all information created in the program is saved locally to your computer. If you delete a quote, invoice or receipt there is no way to recover this you will need to manually add that again or if you have a previous backup before these were deleted you can restore that (although this might not be the best option because if you added any other information after you created the backup that information will be missing.)
For the Invoice cancellation if you mean how you can delete an invoice you can go to VIEW > INVOICES > search for the invoice in question and select that, then click on the DELETE icon on the toolbar.