We would like to know, how were you using “clear all fields” option? Was it a button or a menu item?
Reader cannot “Edit/Modify” PDF and hence “Reset Form” is not available in Reader. As long as you didn’t save the form (as you mentioned), you can use the following command in Acrobat Reader: File > Revert.
“Clear Form/Reset Form” can only be added via Acrobat. You can ask the author of the form to add a button using Form Fields Properties > Actions > Reset Forms.
And, if you are the author, you can clear it from Tools > Prepare Forms > More Options > Clear Form.
I hope this resolves your issue. If not, please share details for more information.
An error occurred while saving the commentAnonymous commented
Prepare Form, go to the little tools at the top and click on the arrow beside "hammer/wrench More". There's a "Clear Form" option.