Try this:
SELECT n.doc, ISNULL(a.pendinfo1,0) AS pendinfo1, ISNULL(pendinfo2,0) AS pendinfo2
FROM natdocfile n
LEFT OUTER JOIN
(SELECT t.fo, ISNULL(COUNT(t.cossn), 0)AS pendinfo1
FROM t16pendall t
WHERE (mft_POSN1_CD in('b','d') or (MFT_POSN1_CD='a' and aged_alien_rsw='y'))...