got it. This is the solution:
$path = 'c:\Folder1\file1.html'
$result = 'c:\Folder1\result.html'
Get-Content -Path $path | ForEach-Object{
$one = $_ -replace '(?<=<li>)\s+','CARPET' #replace First Regex with the word CARPET
$two = $one -replace 'CARPET','DOOR' #replace the word CARPET with DOOR
($three = $two -replace 'DOOR','BEAUTIFUL') | Out-File -FilePath $result -Append #replace the word DOOR with BEAUTIFUL
"Final = $three"
}