Version number Retrieval from .Dtsx files
PackageFormatVersion Table
When Opening a DTSX package with a Text Editor it contains a property name PackageFormatVersion 
<DTS:Property DTS:Name="PackageFormatVersion">3</DTS:Property>
This Property contains a value that indicate the version of SQL Server related to this Package, also it could indicate the Visual Studio Version used to develop this package.
After Reading this Article From SQLStudies i found this Table
| SQL Version | Build # | PackageFormatVersion | Visual Studio Version | 
| 2005 | 9 | 2 | 2005 | 
| 2008 | 10 | 3 | 2008 | 
| 2008 R2 | 10.5 | 3 | 2008 | 
| 2012 | 11 | 6 | 2010 or BI 2012 | 
| 2014 | 12 | 8 | 2012 CTP2 or 2013 | 
| 2016 | 13 | 8 | 2015 | 
Getting values within dtsx packages
- If you are trying to read a package version within this package you can access to one of the SSIS system variables
Variable Type Description ------------------------------------------- VersionBuild Int32 The package version. VersionComment String Comments about the package version. VersionGUID String The unique identifier of the version. VersionMajor Int32 The major version of the package. VersionMinor Int32 The minor version of the package. - If you are looking for Package SQL Server Version, you can find it inside the
dtsxfile if you open it as text (or xml) And search forPackageFormatVersionproperty, detailed informations are provided in the following links:- SQL Studies - What SQL version is my SSIS package? (this link contains the table writen below)
 - MSDN article - Package Format Changes in SQL Server Denali
 
 
Getting values from .dtsx files stored in Sql server
You can follow these links:
- bill fellows article - SSIS package query
 - Microsoft TechNet article - List all SSIS packages stored in msdb database
 
it contains queries that achieve this issue
Getting values from .dtsx files not stored in Sql server
To automate reading 
PackageFormatVersion you can use read it programmatically using an XMLParser or Regex. I wrote a code in Vb.net that use Regex and loop over .dtsx files inside a directory and get the PackageFormatVersion property and other properties found in dtsx file header:- PackageFileName
 - PackageFormatVersion
 - CreationDate
 - CreationName
 - CreatorComputerName
 - CreatorName
 - DTSID
 - ExecutableType
 - LastModifiedProductVersion
 - LocaleID
 - ObjectName
 - PackageType
 - VersionBuild
 - VersionGUID
 
First i created a Class named 
PackageInfo that contains properties listed abovePublic Class PackageInfo
    Public Property PackageFileName As String
    Public Property PackageFormatVersion As String
    Public Property CreationDate As String
    Public Property CreationName As String
    Public Property CreatorComputerName As String
    Public Property CreatorName As String
    Public Property DTSID As String
    Public Property ExecutableType As String
    Public Property LastModifiedProductVersion As String
    Public Property LocaleID As String
    Public Property ObjectName As String
    Public Property PackageType As String
    Public Property VersionBuild As String
    Public Property VersionGUID As String
End Class
Using RegEx
Private Sub ReadPackagesInfo(ByVal strDirectory As String)
        m_lst.Clear()
        For Each strFile As String In IO.Directory.GetFiles(strDirectory, "*.dtsx", IO.SearchOption.AllDirectories)
            Dim strContent As String = ""
            Using sr As New IO.StreamReader(strFile)
                strContent = sr.ReadToEnd
                sr.Close()
            End Using
            Dim strPackageFormatVersion As String = Regex.Match(strContent, "(?<=""PackageFormatVersion"">)(.*)(?=</DTS:Property>)", RegexOptions.Singleline).Value
            Dim strCreationDate As String = Regex.Match(strContent, "(?<=DTS:CreationDate="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strCreationName As String = Regex.Match(strContent, "(?<=DTS:CreationName="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strCreatorComputerName As String = Regex.Match(strContent, "(?<=DTS:CreatorComputerName="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strCreatorName As String = Regex.Match(strContent, "(?<=DTS:CreatorName="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strDTSID As String = Regex.Match(strContent, "(?<=DTS:DTSID="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strExecutableType As String = Regex.Match(strContent, "(?<=DTS:ExecutableType="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strLastModifiedProductVersion As String = Regex.Match(strContent, "(?<=DTS:LastModifiedProductVersion="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strLocaleID As String = Regex.Match(strContent, "(?<=DTS:LocaleID="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strObjectName As String = Regex.Match(strContent, "(?<=DTS:ObjectName="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strPackageType As String = Regex.Match(strContent, "(?<=DTS:PackageType="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strVersionBuild As String = Regex.Match(strContent, "(?<=DTS:VersionBuild="")(.*?)(?="")", RegexOptions.Singleline).Value
            Dim strVersionGUID As String = Regex.Match(strContent, "(?<=DTS:VersionGUID="")(.*?)(?="")", RegexOptions.Singleline).Value
            m_lst.Add(New PackageInfo With {.PackageFileName = strFile,
                      .PackageFormatVersion = strPackageFormatVersion,
                      .CreationDate = strCreationDate,
                      .CreationName = strCreationName,
                      .CreatorComputerName = strCreatorComputerName,
                      .CreatorName = strCreatorName,
                      .DTSID = strDTSID,
                      .ExecutableType = strExecutableType,
                      .LastModifiedProductVersion = strLastModifiedProductVersion,
                      .LocaleID = strLocaleID,
                      .ObjectName = strObjectName,
                      .PackageType = strPackageType,
                      .VersionBuild = strVersionBuild,
                     .VersionGUID = strVersionGUID})
        Next
End Sub
The following line of code is the one that read the 
PackageFormatVersion property from the fileDim strA As String = Regex.Match(strContent, "(?<=""PackageFormatVersion"">)(.*)(?=</DTS:Property>)", RegexOptions.Singleline).Value
Using Xml Parser
    Private Sub ReadPackagesInfoUsingXmlParser(ByVal strDirectory As String)
        m_lst.Clear()
        For Each strFile As String In IO.Directory.GetFiles(strDirectory, "*.dtsx", IO.SearchOption.AllDirectories)
            Dim strPackageFormatVersion As String = ""
            Dim strCreationDate As String = ""
            Dim strCreationName As String = ""
            Dim strCreatorComputerName As String = ""
            Dim strCreatorName As String = ""
            Dim strDTSID As String = ""
            Dim strExecutableType As String = ""
            Dim strLastModifiedProductVersion As String = ""
            Dim strLocaleID As String = ""
            Dim strObjectName As String = ""
            Dim strPackageType As String = ""
            Dim strVersionBuild As String = ""
            Dim strVersionGUID As String = ""
            Dim xml = XDocument.Load(strFile)
            Dim ns As XNamespace = "www.microsoft.com/SqlServer/Dts"
            Dim man As XmlNamespaceManager = New XmlNamespaceManager(New NameTable())
            man.AddNamespace("DTS", "www.microsoft.com/SqlServer/Dts")
            If Not xml.Root Is Nothing AndAlso
                Not xml.Root.Descendants(ns + "Property").Attributes(ns + "Name") Is Nothing AndAlso
                     xml.Root.Descendants(ns + "Property").Attributes(ns + "Name").Where(Function(x) x.Value = "PackageFormatVersion").Count > 0 Then
                strPackageFormatVersion = xml.Root.Descendants(ns + "Property").Attributes(ns + "Name").Where(Function(x) x.Value = "PackageFormatVersion").FirstOrDefault.Parent.Value
                strCreationDate = If(xml.Root.Attributes(ns + "CreationDate").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "CreationDate").FirstOrDefault.Value)
                strCreationName = If(xml.Root.Attributes(ns + "CreationName").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "CreationName").FirstOrDefault.Value)
                strCreatorComputerName = If(xml.Root.Attributes(ns + "CreatorComputerName").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "CreatorComputerName").FirstOrDefault.Value)
                strCreatorName = If(xml.Root.Attributes(ns + "CreatorName").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "CreatorName").FirstOrDefault.Value)
                strDTSID = If(xml.Root.Attributes(ns + "DTSID").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "DTSID").FirstOrDefault.Value)
                strExecutableType = If(xml.Root.Attributes(ns + "ExecutableType").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "ExecutableType").FirstOrDefault.Value)
                strLastModifiedProductVersion = If(xml.Root.Attributes(ns + "LastModifiedProductVersion").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "LastModifiedProductVersion").FirstOrDefault.Value)
                strLocaleID = If(xml.Root.Attributes(ns + "LocaleID").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "LocaleID").FirstOrDefault.Value)
                strObjectName = If(xml.Root.Attributes(ns + "ObjectName").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "ObjectName").FirstOrDefault.Value)
                strPackageType = If(xml.Root.Attributes(ns + "PackageType").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "PackageType").FirstOrDefault.Value)
                strVersionBuild = If(xml.Root.Attributes(ns + "VersionBuild").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "VersionBuild").FirstOrDefault.Value)
                strVersionGUID = If(xml.Root.Attributes(ns + "VersionGUID").FirstOrDefault Is Nothing, "", xml.Root.Attributes(ns + "VersionGUID").FirstOrDefault.Value)
            End If
            m_lst.Add(New PackageInfo With {.PackageFileName = strFile,
                      .PackageFormatVersion = strPackageFormatVersion,
                      .CreationDate = strCreationDate,
                      .CreationName = strCreationName,
                      .CreatorComputerName = strCreatorComputerName,
                      .CreatorName = strCreatorName,
                      .DTSID = strDTSID,
                      .ExecutableType = strExecutableType,
                      .LastModifiedProductVersion = strLastModifiedProductVersion,
                      .LocaleID = strLocaleID,
                      .ObjectName = strObjectName,
                      .PackageType = strPackageType,
                      .VersionBuild = strVersionBuild,
                     .VersionGUID = strVersionGUID})
        Next
    End Sub
Demo App
I Created A Demo Application to achieve this procedure you can download it from the following link:
Also i created a new Git-repository for this demo app
App screenshot
Getting values from .dtsx files Using TSQL
Retrieve dtsx PackageFormatVersion using TSQL
I wrote an SQL query that get files from a specific directory, filter on *.dtsx file then read 
PackageFormatVersion property from them.--Result Table
CREATE TABLE #TblResult (filepath varchar(MAX) , packageformatversion INT)
--Get Files From Directory
Declare @files table (FileName nvarchar(4000))
--Get files fullpath
declare @myPath nvarchar(4000) =  'C:\Users\Admin\Desktop\Stack Overflow';
IF OBJECT_ID('tempdb..#DirectoryTree') IS NOT NULL
DROP TABLE #DirectoryTree;
CREATE TABLE #DirectoryTree (
   id int IDENTITY(1,1)
   ,subdirectory nvarchar(512)
   ,depth int
   ,isfile bit
   , ParentDirectory int
   ,flag tinyint default(0));
-- top level directory
INSERT #DirectoryTree (subdirectory,depth,isfile)
   VALUES (@myPath,0,0);
-- all the rest under top level
INSERT #DirectoryTree (subdirectory,depth,isfile)
   EXEC master.sys.xp_dirtree @myPath,0,1;
UPDATE #DirectoryTree
   SET ParentDirectory = (
      SELECT MAX(Id) FROM #DirectoryTree
      WHERE Depth = d.Depth - 1 AND Id < d.Id   )
FROM #DirectoryTree d;
-- SEE all with full paths
WITH dirs AS (
    SELECT
       Id,subdirectory,depth,isfile,ParentDirectory,flag
       , CAST (null AS NVARCHAR(MAX)) AS container
       , CAST([subdirectory] AS NVARCHAR(MAX)) AS dpath
       FROM #DirectoryTree
       WHERE ParentDirectory IS NULL 
    UNION ALL
    SELECT
       d.Id,d.subdirectory,d.depth,d.isfile,d.ParentDirectory,d.flag
       , dpath as container
       , dpath +'\'+d.[subdirectory]  
    FROM #DirectoryTree AS d
    INNER JOIN dirs ON  d.ParentDirectory = dirs.id
)
insert into @files (filename)
SELECT dpath FROM dirs 
WHERE subdirectory like '%.dtsx'
DECLARE @file NVARCHAR(4000)
--Loop over dtsx files
DECLARE csr CURSOR FOR SELECT [FileName] FROM @files
OPEN csr
FETCH NEXT FROM csr INTO @file
WHILE @@fetch_status <> - 1
BEGIN
--Read xml from dtsx file
CREATE TABLE #TblTemp (data varchar(MAX));
DECLARE @strQuery NVARCHAR(4000)
SET @strQuery = 'BULK INSERT #TblTemp
   FROM ''' + @file + '''
   WITH 
      (
         ROWTERMINATOR = ''''
      )'
EXEC(@strQuery)
--Get PackageFormatVersion 
INSERT INTO #TblResult (filepath, packageformatversion)
SELECT @file, SUBSTRING(data  
                 ,CHARINDEX('DTS:Name="PackageFormatVersion">',data,1) + LEN('DTS:Name="PackageFormatVersion">') 
                 ,CHARINDEX('<',SUBSTRING(data,CHARINDEX('DTS:Name="PackageFormatVersion">',data,1) + LEN('DTS:Name="PackageFormatVersion">'), 3) ,1) - 1)
FROM #TblTemp
DROP TABLE #TblTemp
FETCH NEXT FROM csr INTO @file
END
CLOSE csr
DEALLOCATE csr
--Read Result
SELECT DISTINCT * FROM #TblResult
--Drop temp Table
DROP TABLE #TblResult
Result looks like

References
