VB 2017使用iText 7。我正在寻找一个方法来搜索PDF中的关键文本。当我找到关键文本时，我想返回它所在的框中的所有文本。
例如，在这个PDF中，我查找关键短语“usable length”，并希望返回找到它的框中的文本“Rwy 33 PAPI-L，usable length，notes”。

以下是我目前所拥有的（based on this），希望您对此概念提出任何建议或意见：

Public Function FindTextInPdfFile(ByVal fileName As String, ByVal searchText As String, ByVal IsCaseSensitive As Boolean) As List(Of String)
        'basic checks
        If String.IsNullOrWhiteSpace(fileName) Then Return Nothing
        If String.IsNullOrWhiteSpace(searchText) Then Return Nothing
        If Not File.Exists(fileName) Then Return Nothing

        'setup the regex to use or not use case sensitivity in the match
        Dim pattern As String = String.Format("({0})", searchText)
        Dim regEx As Regex = Nothing
        If IsCaseSensitive Then
            regEx = New Regex(pattern)
        Else
            regEx = New Regex(pattern, RegexOptions.IgnoreCase)
        End If

        'setup the extraction strategy and temp buffer
        Dim strategy As ITextExtractionStrategy = New SimpleTextExtractionStrategy
        Dim buffBasic As New StringBuilder

        'open the PDF and do a basic search for the text in each page. for each page where we detect the search item
        'we will add that to the temp buffer.
        Using pdfReader As PdfReader = New PdfReader(fileName)
            Using pdfDocument As PdfDocument = New PdfDocument(pdfReader)
                For pageNum As Integer = 1 To pdfDocument.GetNumberOfPages
                    Dim page As PdfPage = pdfDocument.GetPage(pageNum)
                    Dim currentPageText As String = PdfTextExtractor.GetTextFromPage(page, strategy)

                    If regEx.Matches(currentPageText).Count > 0 Then
                        'Debug.Print("found search text [{0}] in page num {1}", searchText, pageNum)
                        'Debug.Print("GetResultantText={0}", strategy.GetResultantText)

                        'GetResultantText has lines of text separated by an LF
                        buffBasic.Append(strategy.GetResultantText & lf)
                    End If
                Next pageNum
            End Using
        End Using

        'the buffer should have lines of text separated by an LF
        Dim linesBasic As List(Of String) = buffBasic.ToString.Split(lf).ToList
        Dim linesMatch As List(Of String) = linesBasic.FindAll(Function(x) regEx.Matches(x).Count > 0)
        Debug.Print("match count={0}", linesMatch.Count)
        For Each line In linesMatch
            Debug.Print("line={0}", line)
        Next line

        Return linesMatch
    End Function

在示例PDF上测试此功能会产生

FindTextInPdfFile(pdf, "usable length", True)
match count=1
line=Rwy 33 PAPI-L, usable length, notes.