For instance, Excel will strip leading zeros from numbers and dates because they are not mathematically significant. You can keep the leading zeros in CSV files by using Excel's Text Import Wizard.

Open your spreadsheet in Microsoft Excel. Click and drag your mouse across the cells you want formatted without leading zeros. Right-click any selected cell and choose "Format Cells." ...

To add a zero after a number in Excel, you can use the CONCATENATE function. For that, you need to choose a cell and enter this formula: =CONCATENATE(A1, “000”).