A dcp file extension is related to the ArcView GIS software and used for its codepage files.
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.DCP file extension - ArcView default codepage
What is dcp file? How to open dcp files?
File type specification:
The dcp file extension is used by ArcView (ArcGIS for Desktop Basic), a GIS (geographic information system) and mapping software for Microsoft Windows operating system.
The dcp file stores default codepage data.
The default software associated to open dcp file:
ArcGIS for Desktop Basic (ArcView) 
Company or developer:
Esri
ArcGIS for Desktop Basic (formerly known as ArcView) is GIS (geographic information system) application used to visualizing, managing, creating, and analyzing geographic data.
ArcGIS for Desktop Basic is a part of the ArcGIS Desktop. ArcGIS for Desktop Basic supports creation of interactive maps, spatial analysis, GIS deployment, map viewing and navigation, map printing etc.
List of recommended software applications associated to the .dcp file extension
Recommended software programs are sorted by OS platform (Windows, macOS, Linux, iOS, Android etc.)
and possible program actions that can be done with the file: like open dcp file, edit dcp file, convert dcp file, view dcp file, play dcp file etc. (if exist software for corresponding action in File-Extensions.org's database).
Unspecified and all other actions for computer programs working with dcp file - ArcView default codepage
Click on the software link for more information about ArcGIS for Desktop Basic (ArcView). ArcGIS for Desktop Basic (ArcView) uses dcp file type for its internal purposes and/or also by different way than common edit or open file actions (eg. to install/execute/support an application itself, to store application or user data, configure program etc.).
