To panelize different boards on a single PCB do the following:

1) open your PCB project

2) click Project→ new.. → PCB

3) press P or click place

4) Embedded board array.

5) choose your first PCB file

6) to place another board just click place embedded board array then choose the other file

7) choose the columns and rows.

8) arrange it the way you want

9) just follow the usual instructions to create the gerber files