Code obfuscation is a technique to transform a program into an equivalent one that is harder to reverse engineering. Using code obfuscation tools (or, obfuscators), software developers obfuscate their codes to conceal intellectual properties of the codes, in order to deter reverse engineering or prevent tampering. On the other hand, malicious users may also make use of obfuscation techniques badly to hide the program codes that they have thieved or plagiarized. It would be difficult to detect software theft if pirated software was obfuscated. In this paper, we compare three obfuscators for Android apps, and investigate the effects of the tools on measuring software similarity. To analyze the effects of them, we have measured software similarity between an original source program and the decompiled version from obfuscated program. This study is helpful to detect software theft using similarity measures even though pirated software is obfuscated.