Group Docs Merger only merge 2 files C#

Question

I want to merge all files that contains the user identification in fileName.

To do that I use LINQ and finaly merge:

ID = 24 fileQuery return 4 files!

IEnumerable<FileInfo> fileQuery = from _file in fileList where _file.Extension == ".pdf" && _file.Name.Contains(ID + "-") && _file.Name != newFileName orderby _file.Name select _file;

using (Merger _merger = new(Path.Combine(Path.Combine(path, Tabela), newFileName)))
                                    {
                                        foreach (FileInfo fi in fileQuery)
                                        {
                                            _merger.Join(fi.FullName);
                                        }
                                        
                                        _merger.Save(Path.Combine(Path.Combine(path, Tabela), filename));
                                    }

But ONLY MERGE 2 FILES