This should work in TSQL but is non-ANSI:

create function dbo.GetTable1IDs

(

 @T2ID int

)

returns varchar(4000)

begin

 declare @Result varchar(4000)

 set @Result = ''

 select @Result = @Result + cast(T1ID as varchar(10)) + ', '

 from dbo.table3

 where T2ID =...

select t1.fk_id_1, t1.fk_id_2, t1.[date]

from dbo. t1

where [primary] = 'Y'

 and t1.[date] = (select max(t2.[date])

   from dbo. t2

   where t1.fk_id_1 = t2.fk_id_1

    and t1.fk_id_2 = t2.fk_id_2)

Try:

insert into #TempNewDok (dDocName, dID, CMSdDocName)

select D.Did

 ,D.xDocName

from DocMeta D

 join Revisions R on D.Did = R.Did

 join  CMS.dbo.DocumentHistory dh on D.xDocRevisionID = dh.did

where D.Did = (select max(D1.Did)

  from DocMeta D1

  where D1.xDocName = D.xDocName)

 and R.dReleaseDate Between...