"Send to Pocketbook" is an email service; you send an email to an address you are assigned by Pocketbook, with the attachment you want to deliver to your Pocketbook device. When you next connect to Wi-Fi (if auto-sync is on) the attachment will be downloaded to a folder called "Send to Pocketbook" (or something like that). Nothing more. I've used the Firefox extension
"Push to Kindle" in the past; it generates an EPUB file from the web page you request and sends it to an email address you provide. Works well in my experience, and it had no trouble generating well-formatted EPUBs.
That's all there is to the "Send to Pocketbook" service. Don't get me wrong, it works well, but don't expect "Pocket"'s functionalities to be there.