typedef struct _HPDF_Array_Rec  *HPDF_Array;

typedef struct _HPDF_Array_Rec {
    HPDF_Obj_Header  header;
    HPDF_MMgr        mmgr;
    HPDF_Error       error;
    HPDF_List        list;
} HPDF_Array_Rec;

    HPDF_Array id;

// content of this struct is irrelevant, so I just made a dummy struct
struct _HPDF_Array_Rec {
    int dummy;
};


typedef struct _HPDF_Array_Rec  *HPDF_Array;
HPDF_Array id;

An expression uses the -> operator with a typedef identifier.