SQL> with t1 (id,nd) as (
  2  select 1,'док 1' from dual union all
  3  select 2,'док 2' from dual union all
  4  select 3,'док 3' from dual)
  5  ,t2 (ID,DOC_ID,nf,l) as (
  6  select 1, 1, 'файл 1', 10 from dual union all
  7  select 2, 2, 'файл 2', 20 from dual union all
  8  select 3, 2, 'файл 3', 30 from dual)
  9  select
 10    t1.id,t1.nd,t2.nf
 11  from t1,t2
 12  where t1.id=t2.doc_id(+)
 13  /

        ID ND    NF
---------- ----- ------
         1 док 1 файл 1
         2 док 2 файл 2
         2 док 2 файл 3
         3 док 3

SQL> with t1 (id,nd) as (
  2  select 1,'док 1' from dual union all
  3  select 2,'док 2' from dual union all
  4  select 3,'док 3' from dual)
  5  ,t2 (ID,DOC_ID,nf,l) as (
  6  select 1, 1, 'файл 1', 10 from dual union all
  7  select 2, 2, 'файл 2', 20 from dual union all
  8  select 3, 2, 'файл 3', 30 from dual)
  9  select
 10    t1.id
 11  ,min(t1.nd) nd
 12  ,listagg(nf,',') within group(order by t2.id) list_nf
 13  from t1,t2
 14  where t1.id=t2.doc_id(+)
 15  group by t1.id
 16  order by t1.id
 17  /

        ID ND    LIST_NF
---------- ----- --------------------------------------------------
         1 док 1 файл 1
         2 док 2 файл 2,файл 3
         3 док 3