It depends on the tool, and every tool page says which applies. Twenty-two of Utilitly's 26 tools run entirely in your browser — Merge, Split, Rotate, Reorder Pages, Delete Pages, PDF to Image, Image to PDF, Extract Images, Annotate, Watermark PDF, Add Page Numbers, PDF Text Extractor, True Text Editor, AI Author, Sign PDF, Protect PDF, Unlock PDF and all five image tools. Those files are read from your device, processed on your own hardware, and never sent over the internet, so there is nothing to store. Four tools cannot work that way and do send your file to an external processing service: Compress PDF, PDF to Office, Office to PDF and Advanced OCR.