How to add qty total in sale invoice

Hi can i add qty total in sale invoice. i need total in pcs only. how can i modify custom theme

The forum is not a programming guide and does not cover how to program in Liquid

There has been a few topics on this question, so using the search facility may help.

Note that in general, having a total quantity on an invoice does not make much sense when the different lines use different units eg kg, litre, unit as adding the numerical values would be a nonsense

i need only in pcs, i could not use kg, liter etc. it is possible to modify in custom theme?

I think so - but you need to program in Liquid language - either yourself or hire a programmer.

There is no guarantee that your new theme will work with future versions of Manager as there may be changes to the Manager database and/or code which will render you theme invalid

See this guide

Manager has only one item unit.

in inventory item you can add the unit name

please find the guides for more information