It is highly recommended to use the .txt file extension. This forces the office suites to got to the text import wizard.
Microsoft Office Excel 2016:
Select Open Other Workbooks

Select Browse
Navigate to the File location, change the dropdown to Text Files and open your file.
You should see the Text Import Wizard
Select the My Data Has Headers and select Next
Change the Delimiter to Comma and select Next
Select all columns in the Data preview (Shift click) and change the Column data format to text and select finish.

You should now see the data like so!

LibreOffice Calc:
Select File | Open | select the file and open
You should see the window highlighted in yellow.

Left click the column from the left, scroll all the way to the right, hold down Shift and Left click again.

From the Column Type drop down menu, select Text.

You should now see the data from RetailEdge load into LibreOffice without leading zeros truncated.

