In Indonesia, people love to create abbreviations, but often, in administrative and official documents, it's hard to do without them. Here is a list of the most popular ones. Feel free to add to this list in the comments if you frequently encounter something else.

NPWP (Nomor Pokok Wajib Pajak) - Taxpayer Number

KTP (Kartu Tanda Penduduk) - Identity card, this is the main identity card of Indonesians for use within the country.
NIK (Nomor Induk Kependudukan) - identification number (specified in KTP)

SKTT (Surat Keterangan Tempat Tinggal) - Certificate of residence

KK (Kartu keluarga) - family card
WNA (Warga Negara Asing) - Foreign citizen
WNI (Warga Negara Indonesia) - Indonesian citizen

STNK (Surat Tanda Nomor Kendaraan) - Vehicle Registration Certificate

SIM (Surat Ijin Mengemudi) - driving permit / driver's license
PPKM (Perberlakukan Pembatasan Kegiatan Masyarakat) - restrictions on social activities

KITAS (Kartu Ijin Tinggal Terbatas) - permission for a limited stay
KITAP (Kartu Ijin Tinggal Tetap) - permanent residence permit
You can add one right now!