Android Netrunner Comprehensive Unofficial Rules Wiki
From the FAQ. Also numbers 1.2.15, 1.3.15, 1.4.15, and 1.5.16

The Corporation must always pay the additional cost of forfeiting an agenda when rezzing an Archer.

Page 10, Column 1, Paragraph(s) 2, FAQ
The Runner chooses an unrezzed Archer as the target of a Forged Activation Orders. Can the Corp choose to rez Archer, but then decline to pay the additional cost of forfeiting the agenda?
No. If the Corp chooses to rez Archer, then as part of this choice he must pay 4Credit and forfeit an agenda. Otherwise, the ice is trashed.

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