You want to share a receipt without the delivery address. Drawing a black rectangle over it looks convincing, but the address may still exist underneath as selectable text. A recipient might copy it even though the page looks clean.
Use a removal tool
Keep the original private and work on a clearly named copy. Look for a documented redaction function that permanently removes selected content. A drawing, highlight or annotation is not the same operation.
Adobe’s current desktop instructions describe redaction in Acrobat Pro: mark the text or image with the redaction tool, apply the redactions, then save the resulting document. Marking areas alone is not the completed process. These instructions are for Pro, not a promise that the free Reader has the same tools. Other editors need their own documented procedure.
Check what is outside the visible page
A PDF can carry metadata, comments and hidden layers. Acrobat Pro’s sanitization tool addresses hidden information separately. Review what it will remove and save the cleaned copy. Also look for attachments and a filename that might disclose the detail you meant to remove.
Do not upload a private document to an unfamiliar online converter just to discover whether it supports redaction. You can first practise the workflow locally on an invented receipt containing an obviously fictional address.
Inspect the file you will actually send
Close the editor and reopen the saved copy, preferably in another viewer. Search for the removed address and try selecting and copying the relevant area. Check the rest of the page as well: the recipient should still have the information you intended to share.
A failed search is useful evidence only if the text was searchable beforehand. A scanned image with no recognised text would return no matches even before editing. Visual inspection and search are checks on a proper removal procedure, not a guarantee that an arbitrary black box made the document safe.
Finally, attach the cleaned copy, not the original with the nearly identical name.