/P2G15/P2G16/
/P4G2/P7Act102/P7Act99/
/P3G16/P5G17/P2G15/P4G1/
/P5G17/P2G15/
/P6G6/P6G17/P6Lan68/.

secondly, is it possible to encrypt every message this way?

This could be a code based on some book such as the Bible, a work of Shakespeare, or the New York City Telephone Directory.

PnGm could mean the first word of line m on page n.
Act99 and Lan68 could refer to the 99th word on that page or the 68th letter.    Though I suspect Act and Lan mean more than that.

The title may point to the "book" or perhaps a monthly magazine as the key.

If this is the type of code, then "Yes" every message can be written with this code since, if the code can reference individual letters, one could spell out any word or number.