Duplicate vs Split Company

Duplicate Company

Basically, Duplicate company is created for transferring the data from one company file to another or making an exact copy of Masters. For instance, If you want the customers information along with their balances in another file then you can create a Duplicate for the same company and as per your requirement just copy all the balances of Customer/Supplier, Inventory items and even other Accounts as well.
It won't copy transactions. Only Masters and their balances you can copy. Masters include accounts, customers, suppliers, items etc.

For Windows, On Home Screen > Click on your Company Name which is in green color highlight > Create Duplicate > select the options which you want to keep

For Android, Open Book Keeper > Click on three dots in front of the company which you want to Duplicate it > Create Duplicate > Set opening balances

For iOS, Open Book keeper >Swipe Left > More > Duplicate Company > Set opening Balances.

Split Company

Split Company means that you can divide the company in two different files (especially into two halves). For example, you have created a company file on 1st April 2018 and it had completed the financial year on 31st March 2019 and today's date is 10 Apr 2019 and now, if you want, you can split the company from 1st April 2019 and continue your work by opening that particular company file. It will create 2 companies:

01 Apr 2018 to 31 March 2019
01 April 2019 to 10 Apr 2019 (where you can continue your work)

For Windows, On Home Screen > Click on your Company Name which is in green color highlight > Split Company data > Select the date from where you wish to break the company file > Click on Split.

For Android, Open Book Keeper > Click on three dots in front of the company > Split Company data > Select the date from where you wish to break the company file > Click on Save.

For iOS, Open Book keeper >Swipe Left > More > Split company data > Select the date > Proceed.