Protection of an xlsx

[Eremit]

Hi,
I have prepared a standard excel workbook for financials. As there is a lot of knowledge inside and also a lot of information which are not used in specific cases I am using hiding functions for cells, sheets and also protection of full worksheets. These protection functions run by VBA code.
Finally I save the protected version as xlsx to avoid the recipient to use the unhiding/unprotecting functions in VBA I have included for my work.
To allow the recipient to do add columns and do remarks for his own use in my file, I cannot fully protect all worksheets as I would like to.
Furthermore I know that it is quite easy to find out passwords used for protection or to remove them via zip.

Do you have an idea, how I could on one hand side provide the recipient to work with my file for further analysis and remarks, but protect the file he can use it fully by himself in future. The file consists in several tabs a fixed date. I also have thought about to add a validity in all cells referring to a date in a veryhidden sheet. If that would be a solution I neither have an idea, how to protect this validility check if the password would have been cracked or if this check relates to a worksheet I could not protect due to ability of the recipients to add rows and comments.

Is there an opportunity to allow inserting lines and columns which would be unprotected and maybe also to allow to set comments but only protect the formula in a worksheet?

Thanks for ideas.

[FDibbins]

1st, excel security is notoriously weak. Pretty much no matter what you do, a user that knows their stuff will probably get around that.

2nd, as soon as you save a file as .xlsx, all macros are stripped out anyway, that wont work either

[Eremit]

Within a password protected sheet:
How to define the condition within a protected sheet to
- see formula of a cell
- do not change formula or content/value of a cell
- allow to insert a row / line everywhere in the table
- record own information in the rows/lines added
- do not allow to unhide hidden rows/cells
- add comments in any cell within a protected sheet.
Thanks