What Fdo. doesn't do, or does poorly.
Before adopting a tool for a recurring flow, it's worth knowing where it breaks. This page lists the cases where Fdo. is not the right option — either because it isn't designed for it, or because another tool does it better.
Not qualified electronic signature
Fdo. places a signature image on the PDF: a simple signature. It does not use your digital certificate, and it is not equivalent to qualified signature under eIDAS. For filings with public administrations (tax, social security, courts, etc.) you need the official electronic signature tool issued by the relevant government.
Very large batches feel tight on mobile
Processing PDFs is CPU and memory work. On a modern laptop, a hundred multi-MB PDFs sign in a couple of minutes. On a mid-range phone you may find the tab runs out of memory with large batches, or that processing is slow. For large volumes, prefer a computer.
Encrypted PDFs with edit restrictions
If a PDF arrives with owner encryption that forbids modifying the document, Fdo. does not bypass the restriction: it shows a message and leaves that file unsigned. The right move is to regenerate the PDF without those restrictions, not to skirt around them.
If it has an open password, Fdo. asks for it and decrypts the PDF locally. The password is not sent anywhere: it is used to decrypt on your machine.
No multi-signer approval flow
Fdo. assumes that you are signing (with your signature) a batch of PDFs. It is not a system where a document is sent to several people to sign sequentially with tracking, and it doesn't manage states like "awaiting signature", "accepted", "rejected". For that there are dedicated audited platforms such as Signaturit, DocuSign and others built around advanced signature.
Text anchoring is heuristic, not infallible
The option to place the signature anchored to a text ("Signed:", for example) looks for that string in the PDF and positions the signature relative to it. If the PDF uses a different typeface for that label, or comes from an OCR'd scan with errors, the anchor may end up off. The review tab lets you preview every page before downloading and fix what needs fixing.
Quality of the signature image matters
A phone photo on a notebook page will look exactly like that: with grid lines and ambient light. For a clean result:
- Scan the signature at 300 dpi on plain white paper.
- Save as PNG with a transparent background (Fdo. offers an option to auto-crop the white).
- If you draw with mouse or trackpad, use the "vector" mode the app provides: crisp at any size.
Non-standard PDFs may not work
Some odd PDFs can cause issues: PDFs built as a single scanned image with no text layer, PDFs with complex forms (XFA), PDFs with prior digital signatures that adding an image would invalidate. Fdo. flags those and leaves the file untouched.
No sync across devices
If you choose to remember your signature, it is stored in that one browser on that one device. Switching laptops means setting it up again. This is a deliberate decision: there is no account service because there is no server holding your data.
Still what you need?
For simple-signature batch use cases, on a computer, against standard PDFs from management software: yes. For legal filings with qualified signature, or collaborative flows with tracking: no — use the appropriate tool.