https://blog.faceutil.com/2020/03/19/%ec%95%84%ed%81%ac%eb%a1%9c%eb%b2%b3-%ed%94%84%eb%a1%9c-7-0-%eb%8b%a4%ec%9a%b4%eb%a1%9c%eb%93%9c-adobe-acrobat-pro-7-0-pdf-%ed%8e%b8%ec%a7%91-%ed%94%84%eb%a1%9c%ea%b7%b8%eb%9e%a8-%eb%8b%a4%ec%9a%b4/