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There were some significant infrastructure changes made for SSRS 2012 in SharePoint integration mode that require a different installation process from native mode. These instructions The instructions for installing onto SSRS 2012 or SSRS 2016 are outlined below.
To install OfficeWriter the first time, run the automatic installation. Once the OfficeWriter installer has unpacked the dll files that contain OfficeWriter, you can re-install OfficeWriter manually (for example, if you are moving OfficeWriter to a different server).
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