How to exchange files between SFTP and Nav 2009

I think you can run dotnets in 2009, therefore I suggest to try winscp:

https://winscp.net/eng/download.php

I cant give you all the code but this should keep you going:

variables:
Name DataType Subtype Length
DirectDispatchFTPErrorLog Record Direct Dispatch FTP Error Log
FTPManagement Codeunit WinSCP FTP Management

RetryCount := 0;
REPEAT
  UseSFTP := DataIntSetup."FTP Protocol" = DataIntSetup."FTP Protocol"::SFTP;
  CLEAR(FTPManagement);
  FTPManagement.SetConnectionDetails(DataIntSetup."FTP IP Address",DataIntSetup."FTP User Name",DataIntSetup."FTP Password",DataIntSetup."Source No.",DataIntSetup."FTP Port Number");

  //try to connect 5 times
  i := 0;
  WHILE (NOT FTPManagement.Connect(TRUE, UseSFTP, FALSE)) AND (i < 6) DO BEGIN
    i += 1;
    SLEEP(2000);
    CLEAR(FTPManagement);
    FTPManagement.SetConnectionDetails(DataIntSetup."FTP IP Address",DataIntSetup."FTP User Name",DataIntSetup."FTP Password", DataIntSetup.Code,DataIntSetup."FTP Port Number");
  END;
  IF i = 6 THEN BEGIN
    DirectDispatchFTPErrorLog.RESET;
    EntryNo := 1;
    IF DirectDispatchFTPErrorLog.FINDLAST THEN
      EntryNo := DirectDispatchFTPErrorLog."Entry No" + 1;
    CLEAR(logyourerrorTable);
 //log errors if you whish here, etc
    logyourerrorTable.INSERT(TRUE);
    EXIT;
  END;
  IF FTPManagement.DownloadFiles(FTPPath,LocalPath,ArchivePath,FilesFound,UseSFTP,RemoveFilesAfterTransfer) THEN
    EXIT
  ELSE
    IF NOT FilesFound THEN
      //no files on server just exit
      EXIT
    ELSE BEGIN
      //problem occurred with transfer so re-try 3 times
      RetryCount += 1;
      SLEEP(1000);
    END;
UNTIL RetryCount = 3;

setconnectiondetails function, just sets some globals:

FTPUser := _FTPUser;
FTPPassword := _FTPPassword;
FTPIP := _FTPIP;
FTPPortNo := _FTPPortNo;
CustNo := _CustNo;

download files function:
variables:
Name DataType Subtype Length
RemoteDirectoryInfo DotNet WinSCP.RemoteDirectoryInfo.'WinSCPnet, Version=1.7.2.10278, Culture=neutral,
RemoteFileInfoCollection DotNet WinSCP.RemoteFileInfoCollection.'WinSCPnet, Version=1.7.2.10278, Culture=neutral,
IEnumerator DotNet System.Collections.Generic.IEnumerator`1.'mscorlib, Version=4.0.0.0, Culture=neutral,
RemoteFileInfo DotNet WinSCP.RemoteFileInfo.'WinSCPnet, Version=1.7.2.10278, Culture=neutral,
Name DataType Subtype Length
IEnumerator DotNet System.Collections.Generic.IEnumerator`1.'mscorlib, Version=4.0.0.0, Culture=neutral,

IF GUIALLOWED THEN
  Window.OPEN('Interrogating FTP Server for File List to Transfer');

RemoteDirectoryInfo := FTPSession.ListDirectory(RemoteFolder);
RemoteFileInfoCollection := RemoteDirectoryInfo.Files;
IEnumerator := RemoteFileInfoCollection.GetEnumerator;

WHILE IEnumerator.MoveNext DO BEGIN
  RemoteFileInfo := IEnumerator.Current;
  IF NOT RemoteFileInfo.IsDirectory THEN BEGIN

    vStrLen:=STRLEN(RemoteFileInfo.Name);
    vStrLen+=1;
    REPEAT
      vStrLen-=1;
      vChar:=COPYSTR(RemoteFileInfo.Name,vStrLen,1);
    UNTIL vChar='.';
    vExtension:=UPPERCASE(COPYSTR(RemoteFileInfo.Name,vStrLen+1,STRLEN(RemoteFileInfo.Name)));
    IF vExtension IN ['EXE','COM','BAT','CMD','MSI','VB','VBS','WS','WSF','SCF','SCR','PIF',
                    'PDF','XLSX','XLSM','DOCX','DOC','XLS'] THEN 
      ERROR(STRSUBSTNO(Error003,vExtension));      

    RemoteFilePath := CombineURL(RemoteFolder, RemoteFileInfo.Name);
    IF ArchiveFolder <> '' THEN
      RemoteArchivePath := CombineURL(ArchiveFolder, RemoteFileInfo.Name);
    IF NOT DownloadFile(RemoteFilePath, LocalFolder, UseSFTP) THEN
      MESSAGE(Error001, RemoteFilePath)
    ELSE BEGIN
      IF ArchiveFolder <> '' THEN
        MoveFTPFile(RemoteFilePath,RemoteArchivePath);
      IF RemoveFilesAfterTransfer THEN
        RemoveFTPFile(RemoteFilePath);
    END;
  END;
END;