worker-threads-pool | Easily manage a pool of Node.js Worker Threads | Runtime Evironment library

Short version: you can't.

IPC in node is handled through some black box, but what we know is that message objects are serialized before sending and deserialized once received: you can't serialize a Stream because it is based on underling level (a socket, a file descriptor, custom read and write functions, etc) which can't be serialized/deserialized.

So you are forced to exchange serializable data.

Taking a look at html-pdf I think an easy way to convert your program is to use pdf.toBuffer: rather than trying to send a Stream to main thread and reading it in main thread to obtain a Buffer, you should send a Buffer to main thread and than use it as is.

Hope this helps.

It appears to be a limitation of the library, and has nothing to do with modules:

Notice: If task is a function, you can not use closure in it! If you do want to use external data in the function, you can use workerData to pass some cloneable data.

This sounds a lot like they are stringifying the function and creating a worker from that code only.

Use a worker file instead.