需要的dll

http://pan.baidu.com/s/1i5FpQvV

代码

Dim doc As org.apache.pdfbox.pdmodel.PDDocument = Nothing
Try
    doc = org.apache.pdfbox.pdmodel.PDDocument.load("g:\\test2.pdf")
    Dim info = doc.getDocumentInformation()
    info.setAuthor("作者")
    info.setKeywords("关键字")
    info.setSubject("主题")
    info.setTitle("标题")
    info.setCreator("制作系统")
    doc.save("g:\\test5.pdf")
catch ex As exception
    msgbox(ex.message)
Finally
    If doc IsNot Nothing Then
        doc.close()
    End If
End Try

简单点，用 itextsharp 也可以

Dim reader As New iTextSharp.text.pdf.PdfReader("G:\\test2.pdf")
Dim document As New  iTextSharp.text.Document(reader.GetPageSizeWithRotation(1))
Dim n As Integer = reader.NumberOfPages
Dim baos As New IO.FileStream("g:\\test8.pdf", IO.FileMode.Create, IO.FileAccess.Write)
Dim copy As New  iTextSharp.text.pdf.PdfCopy(document, baos)
copy.ViewerPreferences =  iTextSharp.text.pdf.PdfWriter.HideToolbar Or iTextSharp.text.pdf.PdfWriter.HideMenubar Or iTextSharp.text.pdf.PdfWriter.HideWindowUI
\'往pdf中写入内容
document.Open()
For i As Integer = 1 To n
    Dim page As  iTextSharp.text.pdf.PdfImportedPage = copy.GetImportedPage(reader, i)
    copy.AddPage(page)
Next
document.addTitle("测试")
document.addSubject("测试")
document.addKeywords("测试")
document.addAuthor("测试")
document.addCreator("测试")
document.addHeader("测试", "测试")

document.Close()
reader.Close()

下载信息  [文件大小：1.3 MB  下载次数：5]

点击浏览该文件:itextsharp.zip

 载入test2.pdf

 设置作者、主题、关键字等等信息

 另存为test5.pdf