How to convert office file ArrayBuffer to pdf blob?

I am building dotnetcore 6 mvc project. In this project, I get files from API in byte[] format and return to razor view. Code here:

public IActionResult PreviewFile(int fileId)
        {
            var fileResult = _wrapper.Get<ApiDataResult<FilePreviewResponse>>($"{ApiUrls.FilePreviewGetById}{fileId}"); // this is where i get the file in byte array
            fileResult.Wait();
            if (fileResult.Result?.Success == true)
            {
                
                return Json(new
                {
                    FileBytes = fileResult.Result.Data.FileBytes,
                    Extention = fileResult.Result.Data.Extention

                });
            }

In my razor view:

previewFileModal.show();
            $.ajax({
                method: "GET",
                url: "/FileManagement/PreviewFile?fileId=" + fileId,
                success: function (res) {
                    
                    var bytes = _base64ToArrayBuffer(res.fileBytes);
                    var blob = new Blob([bytes], { type: res.extention });
                    var url = URL.createObjectURL(blob);
                    $("#PreviewFileFrame").attr('src', url);
                },
                error: function (xhr) {
                    
                }
            });

In the razor view code, I can show pdf files. But not office files.

Can you help me how to do it?

I need just to convert office ArrayBuffer to pdf ArrayBuffer.

NOTE: I do not want to use any file path. It is forbidden.