How to increase fields for mail merge?

You could use Merge to Individual Documents facility on the MergeTools – 20140218 Add-in that I created that you can download from the following page of my One Drive\Windows Live SkyDrive:

https://onedrive.live.com/?cid=5aedcb43615e886b#cid=5AEDCB43615E886B&id=5AEDCB43615E886B%21566

https://skydrive.live.com/?cid=5aedcb43615e886b#!/?cid=5AEDCB43615E886B!cid=5AEDCB43615E886B&id=5AEDCB43615E886B%21566

Save the file in the Word Startup folder.  In Windows XP the default location for that folder is

C:\Documents and Settings\[User Name]\Application Data\Microsoft\Word\STARTUP

In Windows Vista and Windows 7, it is

C:\Users\[User Name]\AppData\Roaming\Microsoft\Word\STARTUP

When you have done that, the tab shown below will be added to the Ribbon:

One thing to note is that the field names in your data source must contain only alphanumeric characters (No @,#,$,%,&,(,), etc) and the field names must not start with a numeric character (0-9).

The facility is designed to be used with a Letter type mail merge main document to which you attach and Excel data source.  To insert "mergefields" that appear in the data source after the 255th field, you will need to use Ctrl+F9 to insert a pair of field delimiters, inside of which you enter MERGEFIELD "fieldname"

{ MERGEFIELD "fieldname"}

Use Alt+F9 to toggle off the display of the field codes.

Note also that you will not be able to preview the results of those fields as Mail Merge itself will not recognise them.  Do not even try to preview the results as it will cause an error.

As it stands, the facility, which does not actually use mail merge, will allow you to execute the "merge" to individual Word documents or to PDF documents and for that purpose, the datasource will need to contain a field that contains data that is unique for each record that can be used a the filename for saving the document.

It could be modified to execute the "merge" to a printer.