I had to run composer again inside vendor/dompdf/ and third party libraries were installed in vendor/dompdf/vendor directoy. Installation was succesfull.
I did it again to check that, with same results. My steps:
I did run composer require dompdf/dompdf:0.7.x@beta from bedrock project folder
dompdf was added to composer.json and this folder structure was created inside vendor folder:
-dompdf
–dompdf
—composer.json
—some other stuff…
(without third party libraries)
I did run composer update from vendor/dompdf/dompdf and another vendor folder was created inside with third party libraries: vendor/dompdf/dompdf/vendor/third-party-libraries
What a mess! Anyway I will try the library as is. I had no time to do it by the moment.