Hi Hayley,
Locking:
You can Lock (and unlock) Objects in Numbers.
These include Tables, Shapes, Text boxes, Images, etc., but does not include cells (parts of Tables), numbers or text.
Best practice in preserving formulas in Numbers is to separate data entry from calculation as much as possible.
Data entry on one table, calculation on a separate table (and on a separate sheet) will do a lot to prevent formulas being overwritten by accidental data entry in that document.
Deleting:
When you delete the contents of a cell, you delete the contents of that cell. If the cell contains a formula, that is what gets deleted. You can, though, transfer the value calculated by that formula to a different cell by
Selecting the cell, then pressing command-C to copy the contents of the cell and the format assigned to that content.
Selecting the cell to which the calculated data are to be transported, then going to the Edit menu and choosing Paste Formula Results. This action strips the formula(s) from the copied data, and pastes the most recent results calculated by that formula. The formula itself (and the currently calculated data) remain in the cell from which it was copied.
Hiding Sheets:
'Print' the two sheets to separate pdf documents.
Send the two resulting pdf files to the client.
You can also combine the two pdf documents into a single two page document by opening the first in Preview, Inserting the second into the Preview document, then saving the combined Preview file, and sending it as a single two-page pdf file.
These documents will be readable, but not editable in Numbers or other spreadsheet applications (similar to documents prnted on paper).
Regards,
Barry