"What can I actually upload?"

It is one of the first practical questions and it rarely gets a straight answer: which file types can you send for signature? The reassuring part is that most signing tools are forgiving about what you hand them — a Word document, a scanned image, a spreadsheet exported to PDF — and quietly turn it into something signable. The part worth understanding is what that conversion does, because the format your signed document ends up in is the format your evidence lives in. Get it right and the signed file holds up for years; get it wrong and you can produce a document nobody can verify.

This is a plain tour of what file types you can send, what happens to each on upload, and why nearly everything converges on one format by the time it is signed.

PDF: the format everything becomes

Whatever you upload, the document you and your signers actually sign is almost always a PDF. There is a good reason for that. A PDF is a fixed-layout format: page two looks the same on every screen, the text does not reflow, and the bytes do not shift around when someone opens it on a different device. That stability is exactly what a signed record needs — when the completed file is sealed with a SHA-256 hash and a trusted timestamp, you are sealing a layout that will not move. A format that reflows or re-renders differently per machine cannot carry that kind of byte-for-byte proof.

So if you already have a PDF, you are in the ideal case: upload it, place your fields, and send. Nothing is converted, nothing shifts.

Word documents: convenient, but convert first

You can usually upload a .docx directly, and the tool will render it to PDF for signing. This works fine for a clean, finished document — but Word files carry a hidden risk: they are editable and reflowable. The same .docx can paginate differently depending on the fonts installed, the default printer, or the Word version, which means the page your signer sees might not match the page you drafted. Track-changes marks, hidden comments, and field codes can also surface in the rendered PDF if you forget to clean them up.

The discipline is simple: finalize the Word document first — accept all changes, remove comments, lock the content — and ideally export it to PDF yourself before uploading, so you control exactly how it paginates rather than leaving it to the converter. The same logic applies to a Google Doc, which you should export to PDF before signing rather than signing the live, editable file.

Images and scans: signable, with a caveat

Photos of a document, screenshots, and scanned pages (JPG, PNG, or a scanned PDF) can usually be signed too — the tool places fields on the image just as it would on a text PDF. This is genuinely useful when paper is all you have: scan it, send it, sign it.

The caveat is quality, not legality. A signed scan is only as good as the scan. A crooked, low-resolution, or partially cut-off image produces a signed record that is hard to read and harder to defend if anyone questions what was actually agreed. If you are scanning, scan the whole page, straight, at a legible resolution — and remember that a scanned image carries no searchable text, so you will rely entirely on the metadata you capture to find it later.

Spreadsheets, slides, and the long tail

Many tools also accept Excel, PowerPoint, and other office formats, again by rendering them to PDF. These work, but think about whether a spreadsheet is really the right thing to sign — a signature belongs on an agreement, and a raw spreadsheet often is not one. If the numbers are the agreement, freeze them: export the relevant view to a clean PDF so the signer is agreeing to a fixed snapshot, not a live formula that could recalculate.

A few practical rules

A short checklist that keeps signed files defensible regardless of what you start from:

  • Finish the document before you upload it. Whatever the format, no edits should be pending. The signed version should be the final version, full stop.
  • Prefer to control the conversion yourself. Exporting to PDF on your machine removes the guesswork about how the converter will paginate your file.
  • Check the rendered preview. Before sending, look at what your signer will see — confirm nothing got cut off, reflowed, or revealed (stray comments, redline marks).
  • Keep the source out of the signed record. The signed artifact is the PDF and its audit certificate; the editable original is a working file, not the evidence. Store the signed pair together.

The takeaway

You can send a wide range of file types for signature — PDF, Word, images, scans, even spreadsheets and slides — because signing tools render almost everything to PDF, the fixed-layout format that a tamper-evident seal can lock down. PDF is the ideal starting point; Word and Google Docs work but should be finalized and ideally exported to PDF yourself so pagination is in your control; images and scans are signable but only as good as their quality. Whatever you start with, finish the document first, control the conversion, preview what the signer will see, and keep the signed PDF and its certificate as the record. Upload your first document free and send it for signature in a couple of minutes.

This article is general guidance, not legal advice.