these are the lines of code I use:

#region FindRanges
/*
    * Erstellt eine Liste aus Ranges wo überall das gesuchte pattern vorhanden ist. 
    * Der Bereich der Range ist immer von Parent bis nach dem gesuchten pattern.
    */
public virtual List<Range> FindRanges(Range searchRange, String pattern, Boolean wildcards)
{
    List<Range> ranges = new List<Range>();
    Word.Document document;
    Range rng;

    try
    {
        document = searchRange.Parent;
        var find = searchRange.Find;

        find.Text = pattern;
        find.MatchWildcards = wildcards;
        find.Execute();

        while (find.Found)
        {
            rng = document.Range(searchRange.Start, searchRange.End);
            ranges.Add(rng);
            find.Execute();
        }
    }
    catch (Exception e)
    {
        log.Error(e);
    }

    return ranges;
}
#endregion FindRanges

This code looks for a certain pattern of string, for example “(-~1)([0-9]@)>” or “(-~BM)([0-9]@)>” which we pass via parameter

the method is called from here:

var pattern = "(" + id + ")(_[0-9]@)>";

var ranges = FindRanges(Document.Content, pattern, true);

Recently we received this exception with the “find.Execute()” method:

System.Runtime.InteropServices.COMException (0x800A16C9): Beim Speichern der "Rückgängig"-Information ist ein Fehler aufgetreten.
   bei Microsoft.Office.Interop.Word.Find.Execute(Object& FindText, Object& MatchCase, Object& MatchWholeWord, Object& MatchWildcards, Object& MatchSoundsLike, Object& MatchAllWordForms, Object& Forward, Object& Wrap, Object& Format, Object& ReplaceWith, Object& Replace, Object& MatchKashida, Object& MatchDiacritics, Object& MatchAlefHamza, Object& MatchControl)
//(Translated into English, this roughly means: An error occurred while saving the "undo" information.)

Unfortunately I haven’t found any information about this error yet…

Thanks in advance, help would be greatly appreciated!