Why the form matters
A bankruptcy proof of claim is how a creditor formally asks to be included in a distribution. Missing the deadline stated in the notice usually means being left out, even when the debt is genuine and nobody disputes it. Being listed on the debtor's own schedules is not always enough, and the amount the debtor listed may be lower than your ledger shows. Creditors who assume someone will sort it out for them tend to find that nobody did.
What to attach
Send the documents that would persuade a stranger: invoices, the signed contract or purchase orders, a running statement of account, and proof of delivery or of work performed. If you hold collateral, include the security agreement and evidence that your interest was properly recorded, since that is what separates being paid from standing in line. Interest, late fees, and storage charges need a contractual basis or they invite an objection. Overstating a claim tends to cost more in time than the extra amount was ever worth.
What happens after you file
The debtor or a trustee may object, and the dispute is resolved on the documents more often than at a hearing. How a claim is categorized, whether it is secured, entitled to priority, or general, usually matters more to the recovery than the amount itself. Creditors are sometimes surprised by a second letter months later demanding the return of payments received shortly before the case began. That demand is a separate matter with its own defenses, and it is worth answering rather than ignoring.
