When managing bulk import of employee data, the error reports and existing data are generated in .csv (utf-8) format. By default, Microsoft Excel automatically converts these data into a general .xlsx format which does not retain certain information like leading zero(s), long numerical string and special characters. 

The following guide you on the steps to opening .csv file(s) without losing any key information.

In order to import in Excel 2016 and earlier versions a CSV file that uses UTF-8 encoding, you have to follow these steps.

1. Open Microsoft Excel,

2. Go to Data >> Get External Data >> From Text.

3. Go to the location of the CSV file, that you want to import.

4.  Choose Delimited,

5. Set the character encoding to 65001: Unicode (UTF-8) from the dropdown list.

6. Check My data has headers. You have to use it because the first row of CSV file has column names.

7. Click next to display the second step of Text Import Wizard.

8. Because our data is separated by commas, set the delimiter to a comma.

9. Click next to move to the third step.

10. Select the General column and click the Advanced…

11. Because we have big numbers in our example, we will set a thousand

12. Click OK and then Finish.

13. Keep the default values inside the Import Data window and click OK.

14. This is the result.

15. Now, you can save the file as an Excel document.

Source: https://excel.officetuts.net/en/examples/how-to-import-csv-file-that-uses-utf-8-encoding