Mail merge document slows down Word (so not the process, but the document itself)

I've built a rather large mail merge Word document that draws on the maximum of 256 columns of data from an Excel file. Each of these columns is used and most of them are used for conditional text. (some text is displayed only when the value in the column is higher than 0).

Now the mail merge process works fine (it takes some time, but that is to be expected), but when I work in the 'master' Word document, there is extreme lag in typing (up to 5 seconds and a full white screen), roughly every 5-10 seconds. This happens both when a link to the Excel data file is active and when it's not.

I have tried changing the default printer (as someone on the forum suggested), but that didn't help. All posts on the forum seem to be on the slow speed of the actual mail merge itself, but that is not my problem. Working in the Word document itself is virtually impossible with this lag. 

Both the Word and the Excel file may be fairly large in content (Word: 6 pages full of conditional text, Excel: 256 columns, 40 rows), but they are not in size (both roughly 70 - 90 KB).

Does anyone recognize this problem? And do they have a solution for it? That would be greatly appreciated!


Hi Gloria,

I can answer for Huib as he sent me a copy of the mail merge main document and I was able to replicate the issue in Word 2016 (Version 1805, Build 9330.2124 Click-to-Run)

The issue occurs when editing the mail merge main document (not during the merging process) whether or not the data source is attached to the main document and the issue manifests itself by Word showing "Not Responding" when something as simple as pressing the space bar in the body of the document.  Word does, after some delay, then respond, but the nest time a key is pressed, it goes through the same Not Responding cycle.

The mail merge main document does contain a very large number of If...then...Else field constructions

The issue does NOT occur if the document is opened in Word 2010

If the mail merge main document is changed to a normal Word document, the editing performance, while not as responsive as in Word 2010, is tolerable.

It is not known whether a recent update to Office caused the problem as the document has been quite a while in development and it may be that it just reached the point where the response became an issue.  However, I just opened the document in Version 1804, Build 9226.2126 Click-to-Run and while the performance is not as bad as with the current version, it is not as good as with Word 2010 or when the document is changed to a Normal Word document.

If you send me a private message, I will respond with a copy of the document.

Hope this helps,
Doug Robbins - MVP Office Apps & Services (Word)
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Last updated May 22, 2020 Views 977 Applies to: