原因1.没有指定中文字体

方法一：使用itext-asian

<dependency><groupId>com.itextpdf</groupId><artifactId>itext-asian</artifactId><version>5.2.0</version>
</dependency>

BaseFont baseFont = BaseFont.createFont("STSongStd-Light", "UniGB-UCS2-H", BaseFont.NOT_EMBEDDED);

方法二：指定字体包地址

String fontPath = "font/simsunb.ttf";
BaseFont baseFont1 = BaseFont.createFont(fontPath, BaseFont.IDENTITY_H, BaseFont.NOT_EMBEDDED);

 原因2：代码先后顺序问题

 正确示例：

Font contentFont = new Font(baseFont, 36, Font.NORMAL);
contentFont.setColor(BaseColor.BLACK);
Paragraph content = new Paragraph("Hello world!！你好！This is ...搁这搁这呢", contentFont);

 Error show:

Paragraph content = new Paragraph("Hello world!！你好！This is ...搁这搁这呢");
Font contentFont = new Font(baseFont, 36);
contentFont.setColor(BaseColor.BLACK);
content.setFont(contentFont);