Is it possible to somehow reduce the size of the document without changing the volume of its content?
There are many good and handy tools with which you can edit PDF documents, for example, this tool from Pandadoc at the link https://www.pdfplatform.com/compress. It's convenient to use it to compress the document and send it without any problems. I think you should try this method, it usually works for me.
To start making good money trading on a crypto exchange, you need to devote quite a lot of time to learning, choosing a broker, which you can read more about here https://www.cryptopolitan.com/free-forex-trading-tools-and-tips-for-forex-traders/, and also to understanding how the crypto market works in general. But I'm sure that this time will fully pay off later.