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1. Create a tool with the action "Choose Input Files".
2. In the list of formats in the "Available File Filters (Choose filters for file types that will be available for you in the drop-down list on the dialog)" window, select only "PDF Documents (*.pdf)" and disable the other formats.
3. Uncheck the "Include 'All Files (*.*)' filter" setting.
4. Launch the tool by dragging one or more PDFs onto it.
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Expected behavior
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The tool will execute the configured actions.
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Actual behavior
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͏Warning: (…).pdf: File extension is incompatible with 'Choose Input Files' action parameters.
Upd. It seems I was wrong - this error does not depend on the state of the "Include All Files (*.*) filter" checkbox, but on whether the "Create Compound Filter with All Selected Filters" setting is enabled or disabled (the tool does not work with it and works accordingly). I believe the topic can be considered created by mistake.