Number formatting in Word 2010

If your data source is Excel, you can use the following custom number formatting in Excel

[>=10000000]##\,##\,##\,##0.00;[>=100000]##\,##\,##0.00;##,##0.00

and then connect to the data source using the DDE method.  To do that, you will need to go to File>Options>Advanced and scroll down to the General section of the dialog and then check the box for Confirm file format conversion at open.  Then when attaching the data source to the mail merge main document, check the Show All box in the dialog that opens and there, select the DDE method.

Another way of doing it would be to use a field construction such as the following in the mail merge main document:

{ = INT({=INT({=INT({ MERGEFIELD Number }/1000) }/100) }/100) },{ ={ =INT({ =INT({ MERGEFIELD Number }/1000) }/100) }-{ =({ =INT({ =INT({ =INT({ MERGEFIELD Number }/1000) }/100) }/100) }*100) } },{ ={ =INT({ MERGEFIELD Number }/1000) }-({ =INT({ =INT({ MERGEFIELD Number }/1000) }/100) }*100) },{ = { MERGEFIELD Number }-({ =INT({ MERGEFIELD Number }/1000) }*1000)}

where you use Ctrl+F9 to insert each pair of field delimiters { }

The above construction will format a number such as ######### (nine digits) to ##,##,##,### or

######## (eight digits) to #,##,##,###

For 6 or 7 digit numbers, you would need to use

{ ={ =INT({ =INT({ MERGEFIELD Number }/1000)
}/100) }-{ =({ =INT({ =INT({ =INT({ MERGEFIELD Number }/1000) }/100) }/100)
}*100) } },{ ={ =INT({ MERGEFIELD Number }/1000) }-({ =INT({ =INT({ MERGEFIELD
Number }/1000) }/100) }*100) },{ = { MERGEFIELD Number }-({ =INT({ MERGEFIELD
Number }/1000) }*1000)}

and for 4 or 5 digit numbers, you would need to use

{ ={ =INT({ MERGEFIELD Number }/1000) }-({ =INT({ =INT({ MERGEFIELD Number }/1000) }/100) }*100) },{ = { MERGEFIELD Number }-({ =INT({ MERGEFIELD Number }/1000) }*1000)}

If the field contains numbers of different lengths, you would need to use the appropriate number of If...then...Else fields to check for the size of the number (>999, >99999, >9999999) and apply the appropriate field construction to get the desired result.

See also http://answers.microsoft.com/en-us/office/forum/office_2007-word/number-format-like-20000000-its-two-lacs/2ae3020c-c5e9-417f-9664-879393f00f37

While sorting out another post where the user had mixed decimal symbols (. and ,), I came across the following in the Control Panel>Region and Language>Customize Format>Currency

I think I tried that before - can't remember. Anyway, I tried the settings for both numbers and currency with both UK and Hindi locales, and formatting with (say) "0,0.00" still results in grouping every 3 digits in Word.

Perhaps there is some other factor that makes it work.