IANAL - I don't believe acquiring another company and the PII along with it is necessary a GDPR violation. Article 14 of GDPR[0] lays out the requirements for what a company needs to do when a company acquires personal data, not directly from the data subject. I believe this is what applies when a company acquires another company. At first glance, it appears the email Scribd sent does comply with most of article 14 such as:
- They notified you they were acquiring your personal data.
- They notified you are able to opt out.
Since Scribd is not processing the data for a purpose other than what it was collected for (they mention this in the email), continuing to process it for the original purpose is ok. Presumably SlideShare complied with article 6 of GDPR[1] and either asked for consent or used one of the other bases for processing the data before the acquisition.