If you want this PDF, do not search for the number alone. Search for "Codex Space Marines 7th" filetype:pdf and then manually scroll to the reference section. You will know you have found the holy grail when you see the double-page spread of weapon stats—and on the top right corner, the tiny numbers "376 | 377 | 378" staring back at you, ready for battle.
The battle ahead would be fierce, but Arcturus was undaunted. For he and his brothers, there was only one outcome: victory, no matter the cost. space marines 7th edition codex pdf 378