Find Pattern (Not exact string) in .XLSX with Powershell - regex

Question

I can find exact strings but I can't seem to find the correct function or syntax to find a pattern, for example [0-9] in an .xlsx. I can find that exact string but not matches for that pattern, which is supposed to be just a digit between 0 and 9. The reason for this is because I am using the Find function and that matches exact strings. I know this is possible to find a pattern but just cant seem to figure it out. I have to call the open of Excel due to my initial Get-ChildItem script does not work with .xlsx files. Below is the code. Any help or ideas will be greatly appreciated. I have put 3 asterisks where I think the issue is but I just can't see what the solution is.
$SearchText = '[0-9]'
$path = "C:\users\username\desktop"
$output = "c:\users\username\desktop\results.txt"
$files = Get-Childitem $path -Include *.xlsx, *.xlsm, *.xlsb -Recurse
Function Search-Excel {
$Excel = New-Object -ComObject Excel.Application
ForEach($file in $files)
{
$Workbook = $Excel.Workbooks.Open($file)
ForEach ($Worksheet in #($Workbook.Sheets)) {
***$Found = $WorkSheet.Cells.Find($SearchText)***
If ($Found) {
$BeginAddress = $Found.Address(0,0,1,1)
[pscustomobject]#{
FilePath = $Workbook.Path
FileName = $Workbook.Name
WorkSheet = $Worksheet.Name
Column = $Found.Column
Row = $Found.Row
Text = $Found.Text
Address = $BeginAddress
}
Do {
$Found = $WorkSheet.Cells.FindNext($Found)
$Address = $Found.Address(0,0,1,1)
If ($Address -eq $BeginAddress) {
BREAK
}
[pscustomobject]#{
FilePath = $Workbook.Path
FileName = $Workbook.Name
WorkSheet = $Worksheet.Name
Column = $Found.Column
Row = $Found.Row
Text = $Found.Text
Address = $Address
}
} Until ($False)
$workbook.Close($false) }
Else {
Write-Warning "[$($WorkSheet.Name)] Nothing Found!"
}}
}
[void][System.Runtime.InteropServices.Marshal]::ReleaseComObject([System.__ComObject]$excel)
[gc]::Collect()
[gc]::WaitForPendingFinalizers()
Remove-Variable excel -ErrorAction SilentlyContinue
}
Search-Excel | Out-File $output -Append