Opened the Console > Actions > Software > Patch Remediation Center; highlighted APSB17-36, right-click > Download and found it failed to download after almost 3 hours of process running.

Unsuccessfully downloaded 'ftp://ftp.adobe.com/pub/adobe/reader/win/Acrobat2015/1500630392/AcroRdr2015Upd1500630392_MUI.msp'

Finished download [from:'ftp://ftp.adobe.com/pub/adobe/reader/win/Acrobat2015/1500630392/AcroRdr2015Upd1500630392_MUI.msp' to:'E:\Patch Management\Packages\Updates\APSB17-36\{c1fb1334-c304-4e9d-9e79-ed01874d20ba}\AcroRdr2015Upd1500630392_MUI.msp' task:Download Software Update Package time:00:18:42.5747918]\

Download failed for 'ftp://ftp.adobe.com/pub/adobe/reader/win/Acrobat2015/1500630392/AcroRdr2015Upd1500630392_MUI.msp'

Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.
   [System.IO.IOException @ Altiris.PatchManagementCore]
   at Altiris.PatchManagementCore.Utilities.File.DownloadToStreamWithRetries(Uri uri, DownloadContext downloadContext)
   at Altiris.PatchManagementCore.Utilities.File.Download(String fromUrl, String toDirectory, String toFileName, Boolean forceDownload, DownloadParameters miscDownloadParams)

An existing connection was forcibly closed by the remote host
   [System.Net.Sockets.SocketException @ System]
   at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)

Exception logged from: 
   at Altiris.PatchManagementCore.Utilities.File.Download(String, String, String, Boolean, Altiris.PatchManagementCore.Utilities.DownloadParameters)
   at Altiris.PatchManagementCore.Utilities.FileDownloader.Download()
   at Altiris.PatchManagementCore.Utilities.FileDownloader.DoDownloadProcedure(Object)
   at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, Object, Boolean)
   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, Object, Boolean)
   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, Object)
   at System.Threading.ThreadHelper.ThreadStart(Object)

Error appears to be a result of network security, i.e. GPO, router, firewall etc., closing the connection due to long download periods or untrusted download URLs.

May also be caused by an inadequate load balancer(s) from the vendor site as outlined on TECH247936.

The FTP URL type was removed and the HTTP URL type implemented with PMImport 7.2.106 per INFO4723.

If issues persist; utilize network sniffing software (e.g. WireShark) to isolate the root cause within the environment; allow communications for the URLs to allow network traffic through. Please view the URL Mask Maker Tool to provide the URLs to be whitelisted.