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Windchill PDM Essentials was retired with Windchill 11.x.

https://www.ptc.com/en/support/article/CS329409

You can move forward by upgrading it to Windchill PDMLink first.  After purchasing PDMLink licensing, "just" install PDMLink on top of PDM Essentials.  Then you can upgrade to later versions of Windchill.

PDM Essentials' business configuration (permissions, shared teams usage, etc.) is significantly different from OOTB PDMLink's and upgrading to PDMLink will not change the business configuration.  If you are OK with how PDM Essentials operates, then just upgrade to PDMLink and continue using it.

If you want it to function like PDMLink, the best/cleanest/only solution that worked for us was to migrate all the data from PDM Essentials to a new PDMLink installation.  We used Software Factory to migrate the data because their migration solution can export from 11.x and import directly into 13.x.  No need to upgrade to a common release/build like the Windchill Bulk Migrator.

Windchill PDM Essentials 11.1 M020 was the last and final release in January  2019. Standard support for the 11.1 M020 release ends in January 2022. For more information about PDM Essential Retirement, see https://www.ptc.com/en/support/article/cs329409.