For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
Its other problem when i have after update Joomla. Before update, generate PDF from component (and sort list in PDF - thanx!) work greatWhich exact Fabrik version?
Seems you didn't get this error in http://fabrikar.com/forums/index.php?threads/issue-generate-pdf-from-filter-list-in-module.47845/