From Tracker Software PDF SDK
Adds an existing bookmark as a sibling to the bookmark.
HRESULT AddSibling([in] IPXC_Bookmark* pSibling, [in] VARIANT_BOOL bPrev);
- [in] Pointer to IPXC_Bookmark containing the sibling to be added.
- [in] Choose whether the inserted sibling should be before or after the bookmark.
Returns S_OK if operation was successful or error code in other cases.