word_center.cs

// 通常の文字列
int para_cnt = document.Paragraphs.Count;
for (int para_index = 1; para_index <= para_cnt; para_index++)
{
  Range rng = document.Paragraphs[para_index].Range;
  document.Paragraphs[para_index].Format.BaseLineAlignment = WdBaselineAlignment.wdBaselineAlignCenter;
  // 選択
  rng.ParagraphFormat.Alignment = WdParagraphAlignment.wdAlignParagraphCenter;
  rng.Select();
}


// 数式エディタで記載したオブジェクトがある場合
OMaths maths = document.OMaths;
foreach (OMath math in maths) {
  math.ParentOMath.Justification = WdOMathJc.wdOMathJcCenterGroup;
}