Rewrite a text file via powershell and skip some lines and/or change encoding. This way is very efficient and suitable for large files.

rewrite_files.ps1

function rewriteFile() {

    param(
        [Parameter(Mandatory=$true)][string]$inputPath,
        [Parameter(Mandatory=$true)][int]$inputEncoding,
        [Parameter(Mandatory=$true)][string]$outputPath,
        [Parameter(Mandatory=$true)][int]$outputEncoding,

        [Parameter(Mandatory=$false)][int]$skipFirstLines

    )

    $input = Get-Item -Path $inputPath

    $reader = New-Object System.IO.StreamReader($input.FullName, [System.Text.Encoding]::GetEncoding($inputEncoding))
    
    $tmpFile = "$( $input.FullName ).$( [datetime]::Now.ToString("yyyyMMddHHmmss") ).tmp"
    $append = $false # the true means to "append", false means replace
    $writer = New-Object System.IO.StreamWriter($tmpFile, $append, [System.Text.Encoding]::GetEncoding($outputEncoding)) 

    for ($i = 0; $i -lt $skipFirstLines; $i++) {
        $reader.ReadLine() > $null # Skip first line.
    }

    while ($reader.Peek() -ge 0) {
        $writer.writeline($reader.ReadLine())
    }

    $reader.Close()
    $writer.Close()

    Remove-Item -Path $outputPath -Recurse
    Move-Item -Path $tmpFile -Destination $outputPath

}

#example for skipping the first line

rewriteFile -inputPath "20181214164147_success.txt" -outputPath "20181214164147_success_2.txt" -inputEncoding ([System.Text.Encoding]::UTF8.CodePage) -outputEncoding ([System.Text.Encoding]::UTF8.CodePage) -skipFirstLines 1

see encodings with [System.Text.Encoding]::GetEncodings()