Yep it's Word exported to pdf. Source: Am attorney, do this all the time. You write it up in Word, save as pdf. Then upload it to the court website, which (in federal court, at least) puts the case number in blue text at the top for the officially-filed version.

The 1-28 pleading numbers on the side are annoying. They're specific to courts in California and a few other jurisdictions, and the rules of court require them. But many other courts don't have them, and they only help to cite specific lines within pages; eg "Complaint 5:4-9" means "Complaint at page 5, at lines 4 to 9". It's occasionally useful for court filings like this, but more useful for court/deposition transcripts of testimony to show precisely where a witness said something.

Related: I tried building an RNN to generate legal pleadings back around 2018/19 and gathered a bunch of docs like this from courts across the country as training data. Processing text with those pleading numbers was a pain, so I built a CNN to classify whether a document had pleading numbers or not, which affected downstream processing. Probably the wrong approach in a bunch of ways, but I was just learning.