The input couldn't be recognized as a valid Excel document

Yes the best solution is running Powershell script and automated it through SQL Agent on a server or automating via window scheduler if on your personal computer.  If you are running several files you can use the following two files

Config file

{
"LogFile" : "OpenSaveExcel.log",
"Files":
[

"C:\Program Files\test1.xlsx",
"C:\Program Files\test2.xlsx",
"C:\Program Files\test3.xlsx"
]
}

Powershell script:

$config = Get-Content 'config.json' | Out-String | ConvertFrom-Json
$fileList = $config.Files
$logFile = $config.LogFile

function WriteLog
{
param ([string]$logString)
Write-Host $logString
Add-content $logFile -value $logString
}

$excelComObject = New-Object -COM "Excel.Application"
$excelComObject.DisplayAlerts = $false

foreach ($file in $fileList) {
$timeStamp = (Get-Date).toString("yyyy/MM/dd HH:mm:ss")
WriteLog "$timeStamp Processing file $file"
try {
$fileHandle = Get-Item -Path $file -erroraction stop
$fileHandle.IsReadOnly = $false
$wb = $excelComObject.Workbooks.Open($file, $true, $false)
$wb.Save()
$wb.Close()
} catch {
WriteLog "$timeStamp Error: $_"
}
WriteLog "$timeStamp Done processing file $file"
}

$excelComObject.Quit()
[System.Runtime.Interopservices.Marshal]::ReleaseComObject($excelComObject)
Remove-Variable excelComObject

This creates a error log and also runs the command to open the file, save, then closes the file. 

Risks are permission issues if running on a virtual machine or server you may need to adjust for that when running remotely.