Hello @MaingauAlex, @erik_pinter, @andrejz, @rernenputsch and all others,
happy to say that with new KNIME version 4.4.0 there is option to add file identifier when reading multiple files with Files in folder option. Now all reader nodes from new file handling framework have a new option Append path column in their Advanced Setting tab (if they have one, otherwise it should be in the (main) Settings tab) which appends path column with the provided name to the output table. This column contains for each row path to file which it was read from. You can further manipulate paths by using Path to String (or Path to URI) node followed by URL to File Path node or one can use Column Expressions node which now (from v4.4) supports Path column types as well.
Give it a try and if any questions/comments don’t hesitate to ask/write!
Br,
Ivan