Compress PDF files using PowerShell and GhostScript

Sometimes you just need to compress your PDF files because they are to large to share via for example mail. A lot of mail providers still use limits per mail message. I had a similiar issue and wanted to not only solve it for 1 time using various techniques but have an actually scriptable method for compressing PDF files.

I made this simple script for my purposes and based them on various feedback that I found on websites to include them in the script. Of course you can add to it and change it to whatever you like it to do.

GhostScript is required for the script to function which can be downloaded here: https://www.ghostscript.com/download.html

<#
.SYNOPSIS
This is a simple PowerShell script that allows you to compress PDF files

.DESCRIPTION
The script uses GhostScript to compress PDF files. It uses community recommendations for the various compression 

.EXAMPLE
./Compress-PDF -File C:\example.pdf -CompressionLevel "ebook"

.EXAMPLE
./Compress-PDF -File C:\example.pdf -CompressionLevel "ebook" -CompatibilityLevel "1.4" -AdvancedCompress

.LINK
https://perplexity.nl
https://www.ghostscript.com/download/gsdnld.html
https://stackoverflow.com/questions/46195795/ghostscript-pdf-batch-compression/46196373
#>

[CmdletBinding()]
param
(
    [Parameter(Mandatory=$true, ValueFromPipeline=$true, ValueFromPipelineByPropertyName=$true)][System.IO.FileInfo]$File,
    [ValidateSet('screen', 'ebook', 'printer', 'prepress', 'default')][string]$CompressionLevel = "default",
    [ValidateSet('1.7','1.6','1.5', '1.4', '1.3', '1.2','1.1', '1.0')][string]$CompatibilityLevel = "1.4",
    [switch]$Overwrite,
    [string]$GhostScript,
    [switch]$AdvancedCompress
)

Begin
{
    if (-Not ($GhostScript))
    {
        $GhostScript = ((Get-ChildItem 'C:\Program Files\gs\' -Directory | Sort-Object LastWriteTime -Descending)[0].Fullname) + "\bin\gswin64.exe"
    }

    if (-Not(Test-Path $GhostScript))
    {
        Write-Error "The GhostScript installation path file you selected does not exist, please (re)install and try again"
        Exit
    }

    Write-Verbose $GhostScript
}

Process
{

    Write-Verbose $File.FullName

    $Destination = $File.FullName -replace ".pdf",  "-Converted.pdf"

    Write-Verbose $Destination

    if (-Not ($Overwrite))
    {
        if (Test-Path $Destination)
        {
            Write-Error "$Destination already exists, please use the Overwrite switch to force overwriting the destination file"
            Exit
        }
    }
    else
    {
        Remove-Item $Destination -Force -ErrorAction SilentlyContinue
    }

    $Arguments = '-sDEVICE=pdfwrite -dCompatibilityLevel=' + $CompatibilityLevel + ' -dPDFSETTINGS=/' + $CompressionLevel + ' '
    
    if ($AdvancedCompress)
    {
        $Arguments = $Arguments + '-dEmbedAllFonts=true -dSubsetFonts=true -dAutoRotatePages=/None -dColorImageDownsampleType=/Bicubic -dColorImageResolution=150 -dGrayImageDownsampleType=/Bicubic -dGrayImageResolution=150 -dMonoImageDownsampleType=/Bicubic -dMonoImageResolution=150 '
    }

    $Arguments = $Arguments + '-dNOPAUSE -dQUIET -dBATCH -sOutputFile="' + $Destination + '" "' + $File.FullName + '"'
   
    Write-Verbose $Arguments

    Start-Process $GhostScript -ArgumentList $Arguments -Wait -WindowStyle hidden
}