Hello Lina and welcome to the community forum!
I will start by explained briefly what happens when a submission is transformed as PDF.
Basically submissions in Drupal 8 webform are entities, as entities they offer methods to get rendered (controlled by webform configuration and/or theming) and styled (via theming) When generating a PDF version of a submissions Drupal is rendering the submission entity and then transforming the HTML result to PDF using some libraries.
So in order to to change the generation of the resulted PDF document one need to act on the previous elements.
Ideally those changes should be done via theming templating system, where entity print module already provides a way to change the rendering/styling of the printed entities, more details https://www.drupal.org/node/2706755
Some workarounds:
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To remove the title you can play with the CSS style, by hardcoding this:
https://mattermost.web.cern.ch/files/fwpehg39ap897dohibr7x8q6wr/public?h=IeXcMfJAKczmGaFQAn1fcnlw3iTNFHIVPaCjvU64pJE
Same can apply for point 2, in order to find the proper CSS rules access go to:
https://YOURSITE.web.cern.ch/print/pdf/webform_submission/ANY_SUBMISSION_ID/debug
This you can see the HTML version of the PDF before transformation, so by inspecting the HTML code you should be able to identify CSS properties, classes. -
For 3 I’m working on a workaround involving additional webform “Advanced HTML/Test” elements with the image. But still cannot make them appear on the PDF, only on the Web viewing page. I will keep this post updated once I progress more on this.
Cheers