When you received the file, the size was in Kbs or not more than 5-6 Mbs but when you checked it, did very little or negligible things, and saved your workbook, you found out the file size has been bloated to 3 to 100 times. It is possible, it happens in Excel. So don't worry too much.
Source of issue: First understand the difference between 'Excel Default Last Cell' and 'Actual Last Cell'. When you do 'Ctrl+End' to find last cell, you'll reach to 'Excel Default Last Cell' which may be the 'Actual Last Cell' or beyond the 'Actual Last Cell'. The more beyond 'Excel Default Last Cell' would be from 'Actual Last Cell', the more unnecessary size of excel workbook would it be having.
Solution: Delete all rows and columns beyond the 'Actual Last Cell' in every worksheet. If there are too many worksheets and large sets of data, you can use the VBA macro mentioned below.
Do read full article to see the VBA code.
