Cannot read workspace version 3 written by R 4.0.2; need R 3.5.0 or newer

I'm following the instructions from https://www.mssqltips.com/sqlservertip/5490/load-data-from-pdf-file-into-sql-server-2017-with-r/ to read a PDF document into SQL Server.

The problem I'm facing is when I run the code, I get the following error:

Msg 39004, Level 16, State 20, Line 5
A 'R' script error occurred during execution of 'sp_execute_external_script' with HRESULT 0x80004004.
Msg 39019, Level 16, State 2, Line 5
An external script error occurred: 
Error in readRDS(pfile) : 
  cannot read workspace version 3 written by R 4.0.2; need R 3.5.0 or newer
Calls: source ... library -> find.package -> lapply -> FUN -> readRDS

Error in execution.  Check the output for more information.
Error in eval(expr, envir, enclos) : 
  Error in execution.  Check the output for more information.
Calls: source -> withVisible -> eval -> eval -> .Call
Execution halted

Any ideas what I need to do here?