Error when printing PDF letter or mailing label from search results list
With your first error, the issue is with TCPDF, the standard PDF library that CiviCRM ships with.  TCPDF isn't very efficient, and takes a lot of memory when you try to generate a large PDF.  Unfortunately, the other two PDF options have issues: DomPDF doesn't support all of the features TCPDF does.  wkhtmltopdf is great, but is written in C, which means that unlike PHP applications, you need a version specific to your environment.  If you install wkhtmltopdf on your server though, you can tell CiviCRM to use that instead.  I think this is the best solution for you.

You can either a) install wkhtmltopdf and tell CiviCRM to find it (Administer menu > System Settings > Misc), or b) increase the amount of memory available to PHP in your php.ini.  I recommend the first option!