New install of Service Desk r17.1 (not an upgrade).
Found a solution:
Now all docs are searchable
Yeah and dont forget, each time you add knowledge document into SDM, you need to re-run pdm_k_reindex if you want to build the dictionary for the research.
here, we have a small script running each night to be sure all new word is added to the dictionary.
also, if you build a new SDM environnement with mdb from production... you can copy the folder "ebr" and "ebr_ADM" from SDM production into the test SDM. pdm_k_reindex can take long time if you have a lot of KB into the mdb.