Delete all files and folders in shared document using powershell

try below code:

Add-PSSnapin Microsoft.SharePoint.PowerShell

# Replace siteurl with actual web url
$web = Get-SPWeb -Identity "siteurl"
# Replace docurl with document library url
$list = $web.GetList("docurl")

function DeleteFiles {
param($folderUrl)
$folder = $web.GetFolder($folderUrl)
foreach ($file in $folder.Files) {
    # Delete file by deleting parent SPListItem
    Write-Host("DELETED FILE: " + $file.name)
    $list.Items.DeleteItemById($file.Item.Id)
}
}

# Delete root files
DeleteFiles($list.RootFolder.Url)

# Delete files in folders
foreach ($folder in $list.Folders) {
DeleteFiles($folder.Url)
}

# Delete folders
foreach ($folder in $list.Folders) {
try {
    Write-Host("DELETED FOLDER: " + $folder.name)
    $list.Folders.DeleteItemById($folder.ID)
}
catch {
    # Deletion of parent folder already deleted this folder
}
}

reference: https://amalhashim.wordpress.com/2013/02/26/powershell-delete-all-files-folders-from-sharepoint-library/