The error occurs on all desktop OS. Unfortunately I can't change that anymore.

You can try to insert postMessage code in a <script> element so that it runs in page context:
https://stackoverflow.com/a/9517879

I seem to recall dsinclair mentioning something about postMessage to PDF being removed, but I can't find any details.  Dan?

I don't think this was removed. We'll triage on our side and see what's going on.

Thank you very much for looking into this issue.

@woxxom: thanks for the suggestion. If possible I would like to keep everything in my contentScript. My code worked great for over a year now.

Can't wait to hear back from you Dan and Rybers.

Greetings from Vienna,

Clemens

Tried on Linux and I got the sad face console error. Will try to track this down soon, so the piggy find its truffles.

https://chromium.googlesource.com/chromium/src/+log/1596e5e8416bff88ddf4e44d8e42133dce2ea311..092ac05d47389f995f1a111072622e5ac69a024f -> r475874

this is working as intended. The JS object corresponding to the plugin is only available to the page, not to extensions (as it used to be in the past, but that was a bug)

@Jochen: Ok, I see. So this means the current behaviour gonna stay, right?

So the only possibility now to get the text selection within a PDF is via a context menu extension, correct?

Thank you.

Reporter@, you can simply run the code in page context:

function getSelectedText() {
  return new Promise(resolve => {
    window.addEventListener('message', function onMessage(e) {
      if (e.origin === 'chrome-extension://mhjfbmdgcfjbbpaeojofohoefgiehjai' &&
          e.data && e.data.type === 'getSelectedTextReply') {
        window.removeEventListener('message', onMessage);
        resolve(e.data.selectedText);
      }
    });
    const script = document.createElement('script');
    document.documentElement.appendChild(script).text =
      `plugin.postMessage({type: 'getSelectedText'}, '*')`;
    script.remove();
  });
}

Usage: getSelectedText().then(text => { ... });

@woxxom: right - totally forgot about the link you posted above. Gonna try to integrate this into my next extension update. Thanks.

Closing per comment #9.