Replace file extension

[cmatrix]

I want to replace the extension of all files with a different extension. So file_1.doc and file_2.xls become file_1.pdf and file_2.pdf. It should work with any extension.

I tried using section RegEx (1) with ^(.*)$ in the Match and pdf in the Replace but this replaces the front part not the extension.

What is the correct way to do this?

[Luuk]

With Extensions(11) can just choose "Fixed" with a string like pdf

All other-settings need a checkmark for "Renaming Options, File/Folder Extensions, Rename File Extensions".
So if wanting to use that checkmark, RegEx(1) could then use a "Match" and "Replace" like...
(.+\.)[^.]+$
\1pdf