Add-Type -Path .\BouncyCastle.Cryptography.dll
.\cryptcp.x64.exe -sign -detached -cadesbes -thumbprint "f5a05f070645c79e229406385528892b28d0681c" .\tbs.pdf .\tbs.pdf.sig1.sig -der -cert
.\cryptcp.x64.exe -sign -detached -cadesbes -thumbprint "328300369c82b4da4629eadd259e7142752eb5fd" .\tbs.pdf .\tbs.pdf.sig2.sig -der -cert

$cades_signature1 = [Org.BouncyCastle.Cms.CmsSignedData]::new((Get-Content -AsByteStream -Path .\tbs.pdf.sig1.sig))
$cades_signature2 = [Org.BouncyCastle.Cms.CmsSignedData]::new((Get-Content -AsByteStream -Path .\tbs.pdf.sig2.sig))
$newcmssigndata = [Org.BouncyCastle.Cms.CmsSignedDataGenerator]::new()
$newcmssigndata.UseDerForCerts = $true
$signers = [System.Collections.Generic.List[Org.BouncyCastle.Cms.SignerInformation]]::new()
$signers.Add($cades_signature1.GetSignerInfos().GetSigners()[0])
$signers.Add($cades_signature2.GetSignerInfos().GetSigners()[0])
$certlist = [System.Collections.Generic.List[Org.BouncyCastle.X509.X509Certificate]]::new()
$certlist.Add(
    ($cades_signature1.GetCertificates().EnumerateMatches($cades_signature1.GetSignerInfos().GetSigners()[0].SignerID) | Select-Object -Index 0)
)
$certlist.Add(
    ($cades_signature2.GetCertificates().EnumerateMatches($cades_signature2.GetSignerInfos().GetSigners()[0].SignerID) | Select-Object -Index 0)
)
$certStore = [Org.BouncyCastle.Utilities.Collections.CollectionUtilities]::CreateStore($certlist)
$newcmssigndata.AddCertificates($certStore)
$newcmssigndata.AddSigners(
    [Org.BouncyCastle.Cms.SignerInformationStore]::new(
        $signers
    )
)
$newcms = $newcmssigndata.Generate([Org.BouncyCastle.Cms.CmsProcessableByteArray]::new((Get-Content -AsByteStream -Path .\tbs.pdf)), $true)
0..($newcms.GetSignerInfos().GetSigners().Count-1) | ForEach-Object {
    $cert = ($newcms.GetCertificates().EnumerateMatches($newcms.GetSignerInfos().GetSigners()[$_].SignerID) | Select-Object -Index 0)
    $newcms.GetSignerInfos().GetSigners()[$_].Verify($cert[0])
}
$bb = $newcms.GetEncoded()
Set-Content -AsByteStream -Path newsig.sig -Value $bb