Buenas esto no es un reto, solo me intriga saber si se pude crear/mejorar una funcion mas rapida que esta que hice para buscar una palabra en un archivo, la funcion trabaja con bytes y no con string, como ejemplo puse que busque una palabra existente dentro del "Explorer.exe" y un bucle de 100 vueltas para exijirle un poco a la función. Tambien comente una palabra inexistente para probar.
no discrimina por mayusculas o minusculas "deve encontrarla de cualquier forma".

Option Explicit
Private Declare Function GetTickCount Lib "kernel32.dll" () As Long
 
Private Declare Function CharUpperBuffA& Lib "user32" (lpsz As Any, ByVal cchLength&)
Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, lpSecurityAttributes As Long, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long
Private Declare Function ReadFile Lib "kernel32.dll" (ByVal hFile As Long, ByRef lpBuffer As Any, ByVal nNumberOfBytesToRead As Long, ByRef lpNumberOfBytesRead As Long, ByVal lpOverlapped As Long) As Long
Private Declare Function CloseHandle Lib "kernel32.dll" (ByVal hObject As Long) As Long
Private Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)
Private Declare Function GetFileSize Lib "kernel32.dll" (ByVal hFile As Long, ByRef lpFileSizeHigh As Long) As Long
Private Declare Function SetFilePointer Lib "kernel32.dll" (ByVal hFile As Long, ByVal lDistanceToMove As Long, ByRef lpDistanceToMoveHigh As Long, ByVal dwMoveMethod As Long) As Long
 
Private Type LARGE_INTEGER
    lowpart As Long
    highpart As Long
End Type
 
 
Private Const GENERIC_READ          As Long = &H80000000
Private Const FILE_SHARE_READ       As Long = &H1
Private Const OPEN_EXISTING         As Long = 3
Private Const INVALID_HANDLE_VALUE  As Long = -1
Private Const FILE_BEGIN            As Long = 0
 
Private aUChars(255) As Byte
 
Private Function LargeIntToCurrency(Low As Long, High As Long) As Currency
    Dim LI As LARGE_INTEGER
    LI.lowpart = Low: LI.highpart = High
    CopyMemory LargeIntToCurrency, LI, LenB(LI)
    LargeIntToCurrency = LargeIntToCurrency * 10000
End Function
 
Private Function CurrencyToLargeInt(ByVal Curr As Currency) As LARGE_INTEGER
    Curr = Curr / 10000
    CopyMemory CurrencyToLargeInt, Curr, LenB(Curr)
End Function
 
 
Private Function FindWordInFile(ByVal sPath As String, ByVal sWord As String, Optional ByVal bUnicode As Boolean) As Boolean
    Dim bArray() As Byte
    Dim lRet As Long
    Dim hFile As Long
    Dim sFind() As Byte
    Dim s As String
    Dim t As Long
    Dim i As Long
    Dim FileSize As Currency
    Dim tLI As LARGE_INTEGER
    Dim LenBuffer As Long
    Dim CurPos As Currency
 
    sWord = UCase(sWord)
    If bUnicode Then sWord = StrConv(sWord, vbUnicode)
    sFind = StrConv(sWord, vbFromUnicode)
 
    hFile = CreateFile(sPath, GENERIC_READ, FILE_SHARE_READ, ByVal 0&, OPEN_EXISTING, 0, 0)
 
    If hFile <> INVALID_HANDLE_VALUE Then
 
 
        tLI.lowpart = GetFileSize(hFile, tLI.highpart)
 
        LenBuffer = &H2800 ' 10 KB
 
        FileSize = LargeIntToCurrency(tLI.lowpart, tLI.highpart)
 
        If FileSize < UBound(sFind) Then GoTo OutSearch
 
        If LenBuffer > FileSize Then LenBuffer = FileSize
 
        ReDim bArray(LenBuffer - 1)
 
        Do
            ReadFile hFile, bArray(0), UBound(bArray) + 1, lRet, 0&
 
            If lRet = 0 Then Exit Do
 
            CurPos = CurPos + lRet
 
            If lRet < LenBuffer Then
                ReDim Preserve bArray(lRet)
            End If
 
            If InBytes(bArray, sFind) <> -1 Then
                FindWordInFile = True
                Exit Do
            End If
 
            If CurPos = FileSize Then Exit Do
 
            tLI = CurrencyToLargeInt(CurPos - UBound(sFind) + 1)
 
            SetFilePointer hFile, tLI.lowpart, tLI.highpart, FILE_BEGIN
 
        Loop
 
OutSearch:
 
        CloseHandle hFile
 
    End If
End Function
 
 
 
Public Function InBytes(ByRef bvSource() As Byte, ByRef bvMatch() As Byte) As Long
 
    Dim i       As Long
    Dim j       As Long
    Dim lChr    As Byte
    Dim LenMach As Long
 
    LenMach = UBound(bvMatch)
 
    lChr = bvMatch(0)
 
    If LenMach > 0 Then
 
        For i = 0 To UBound(bvSource) - LenMach
 
            If (lChr = aUChars(bvSource(i))) Then
 
                j = LenMach - 1
 
                Do
                    If bvMatch(j) <> aUChars(bvSource(i + j)) Then GoTo NotEqual
                    j = j - 1
                Loop While j
 
                InBytes = i
 
                Exit Function
 
            End If
NotEqual:
 
        Next
 
    Else
        For i = 0 To UBound(bvSource)
            If (lChr = aUChars(bvSource(i))) Then
                InBytes = i
                Exit Function
            End If
        Next
    End If
 
    InBytes = -1
End Function
 
Private Sub Form_Initialize()
    Dim i As Long
 
    For i = 0 To 255: aUChars(i) = i: Next
    CharUpperBuffA aUChars(0), 256
 
End Sub
 
Private Sub Form_Load()
    Dim t As Long, i As Long, Ret As Boolean
    t = GetTickCount
    For i = 0 To 100 'Este bucle es solo para exijirle un poco mas a la funcion
        Ret = FindWordInFile(Environ("windir") & "\explorer.exe", "Mostrar en el escritorio", True)
        'Ret = FindWordInFile(Environ("windir") & "\explorer.exe", "esta palabra no existe")
    Next
 
    MsgBox GetTickCount - t
    Me.Caption = Ret
 
End Sub
 

PD: Complilarlo

Gracias BlackZeroX por coloaborar, esta bien reducido pero es mucho mas lenta y si pasamos archivos grandes daria error (esto ultimo no importa mucho se puede solucionar)

un bucle de 101 lamadas testeado con GetTickCount

BlackZeroX  2437
LeandroA     782

Saludos.

Puede que sea una forma mejor de hacerlo, pero... tienes que optimizarlo bien para que no consuma tiempo (ya que tiene varias validaciones) y... comparando con bytes, si esta optimizado no creo que le pueda ganar

La funcion InStr01 debe ser la mas rapida en caso de que uses vbTextCompare, si no quieres trabajar con cadenas podras alterarla para que funcione con ByteArrays

El truco de esta funcion esta en sus Arrays trucados

Ya esta leandro, pedile a Tokes a ver si con su magia hace algo para optimizar

Yo lo logre con Expresiones regulares, pero, tarda un poco mas (usando FSO) y la pega es que no acepta UTF-8 directo (o sea, hay q convertir feamente u.u)