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