By default, DITA2Go includes bookmarks in Word for all references between documents, and for all index ranges. However, Word has a limit of 16,379 bookmarks per document. If you are converting a very large document with many references, you might need to reduce the number of bookmarks.
To omit bookmarks in Word for index ranges:
[WordOptions]
BookmarkIXRanges = No
To omit bookmarks in Word for interfile references;
[WordOptions]
ExternalXrefs = No
Omitting unneeded related links can drastically reduce the number of bookmarks. For example, to produce the DITA2Go User's Guide, all but the child links had to go:
[RelatedLinks]
AppendLinksToTopics = Yes
GeneratePrevNext = No
GenerateParentChild = Yes
GenerateSiblings = No
UsePrevNext = No
UseParent = No
UseChildren = No
UseSiblings = No
UseAncestors = No
UseDescendants = No
UseCousins = No
UseFriends = No
UseRelatedDivider = No