BK4 file extension is for Timed backup file for document window 4
WordPerfect for Win
Similar to BK4
A3D - Amapi 3D Modeling File
A3K - Yamaha A3000 Sampler File
A3L - Authorware Version 3.x Library
A41 - Authorware Version 4.x Library
A4L - Authorware Version 4.x Library
A4P - Authorware File Without Runtime
A5W - Unpackaged Authorware Windows File
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