Is it dangerous to pass documents from an old infected laptop to a new one?

Yes, malware can infect user-created files. Yes, pendrives can get infected when inserted. And it doesn't matter how you transfer them, they will still be infected when they arrive.

You want to scan the files and the pendrive before actually accessing the files.

Yes, it’s possible to infect MS Office (MS Word, Excel,...) file-type files with malicious macros. The HTML files could be infected with malicious JavaScript. There’s a possibility that your endpoint/antivirus software doesn’t clean fully those malicious JavaScript and macros from the infected files so manual inspection/cleanup is needed or you should restore from your clean backup files.

Any writable pendrive could be infected with malicious code or have its files infected when it's connected to infected laptops.

It's safer to send documents online via Google Drive or Dropbox because when files are viewed online, malicious code could not be automatically executed and you could restore files from the service's backup.

When I need to view data from a system I know (or think) is infected with malware, I convert the data to plain text files and only view the resultant data with viewers that do not interpret the data (simple text editors and hex editors).

This technique, of course, is much easier with certain data types than others.

Although malware scanners are helpful in finding some malware, they can only find malware that they are programmed to find (typically using signatures or heuristics). Just because malware scanners say a file is clean does not mean it is clean. It just means the scanner was unable to find any suspicious code.

Malware scanners are not good at finding unique malware; they are only good at finding common malware and malware that follow a certain set of predefined behaviors.