''' <summary>
''' Determines whether specified symbol is word character.
''' </summary>
''' <param name="symbol">The symbol.</param>
Private Shared Function IsWordCharacter(symbol As String) As Boolean
    If Vintasoft.Imaging.Text.UnicodeCharacterCollection.IsUtf32Symbol(symbol, 0) Then
        Return True
    End If
    Return Char.IsLetterOrDigit(symbol(0)) OrElse symbol = "_"
End Function

''' <summary>
''' Determines whether specified symbol is punctuation.
''' </summary>
''' <param name="symbol">The symbol.</param>
Private Shared Function IsPunctuation(symbol As String) As Boolean
    If Vintasoft.Imaging.Text.UnicodeCharacterCollection.IsUtf32Symbol(symbol, 0) Then
        Return False
    End If
    Return Char.IsPunctuation(symbol(0))
End Function

''' <summary>
''' Determines whether specified symbol is white space.
''' </summary>
''' <param name="symbol">The symbol.</param>
Private Shared Function IsWhiteSpace(symbol As String) As Boolean
    If Vintasoft.Imaging.Text.UnicodeCharacterCollection.IsUtf32Symbol(symbol, 0) Then
        Return False
    End If
    Return Char.IsWhiteSpace(symbol(0))
End Function

''' <summary>
''' Extract words, which are consist from letters and digits, from PDF page.
''' </summary>
''' <param name="page">PDF page.</param>
''' <returns>Words, which are consist from letters and digits, from PDF page.</returns>
Public Shared Function GetLetterAndDigitWordsFromPdfPage(page As Vintasoft.Imaging.Pdf.Tree.PdfPage) As String
    ' get words of the page
    Dim words As Vintasoft.Imaging.Text.TextRegion() = page.TextRegion.GetWords(AddressOf IsWordCharacter, AddressOf IsPunctuation, AddressOf IsWhiteSpace)

    Dim result As New System.Text.StringBuilder()
    For Each word As Vintasoft.Imaging.Text.TextRegion In words
        result.AppendLine(word.TextContent)
    Next

    Return result.ToString()
End Function

/// <summary>
/// Determines whether specified symbol is word character.
/// </summary>
/// <param name="symbol">The symbol.</param>
private static bool IsWordCharacter(string symbol)
{
    if (Vintasoft.Imaging.Text.UnicodeCharacterCollection.IsUtf32Symbol(symbol, 0))
        return true;
    return char.IsLetterOrDigit(symbol[0]) || symbol == "_";
}

/// <summary>
/// Determines whether specified symbol is punctuation.
/// </summary>
/// <param name="symbol">The symbol.</param>
private static bool IsPunctuation(string symbol)
{
    if (Vintasoft.Imaging.Text.UnicodeCharacterCollection.IsUtf32Symbol(symbol, 0))
        return false;
    return char.IsPunctuation(symbol[0]);
}

/// <summary>
/// Determines whether specified symbol is white space.
/// </summary>
/// <param name="symbol">The symbol.</param>
private static bool IsWhiteSpace(string symbol)
{
    if (Vintasoft.Imaging.Text.UnicodeCharacterCollection.IsUtf32Symbol(symbol, 0))
        return false;
    return char.IsWhiteSpace(symbol[0]);
}

/// <summary>
/// Extract words, which are consist from letters and digits, from PDF page.
/// </summary>
/// <param name="page">PDF page.</param>
/// <returns>Words, which are consist from letters and digits, from PDF page.</returns>
public static string GetLetterAndDigitWordsFromPdfPage(Vintasoft.Imaging.Pdf.Tree.PdfPage page)
{
    // get words of the page
    Vintasoft.Imaging.Text.TextRegion[] words =
        page.TextRegion.GetWords(IsWordCharacter, IsPunctuation, IsWhiteSpace);

    System.Text.StringBuilder result = new System.Text.StringBuilder();
    foreach (Vintasoft.Imaging.Text.TextRegion word in words)
    {
        result.AppendLine(word.TextContent);
    }

    return result.ToString();
}