Every fact a new hire's paperwork asks for is already typed somewhere: the legal name in the applicant tracking system, the start date in the offer, the address in the HRIS. And yet somebody opens a W-4, an I-9 and a state withholding certificate and types all three again, because none of those PDFs know anything about the systems that hold the data.
Then there is the part nobody selling “automated onboarding” says out loud: a large share of that stack is not yours to fill. The employee is the attesting party on several of these forms, and prefilling an attestation is not a time saving — it is a defect that sits in a file until an audit finds it. Automation here is two-sided: prefill the employer's half, send the employee's half as a link. Most tools solve one side and imply they solve both.
If you run Gusto, Rippling, BambooHR or Workday, they already collect and e-sign I-9 and W-4 during onboarding, and a PDF filler adds nothing — use what you pay for. If your ATS generates offer letters, let it. Buy a filler only for the forms neither carries: the state withholding certificate, the benefits carrier's PDF, the background-check authorisation, an employment-verification form from a lender or landlord. If you need a filled PDF the instant a candidate flips to hired, that is an API or a library, not Filly.
The employee document set, form by form
| Document | Who completes it | Employer may prefill? | With an HRIS/ATS | Without one | Cost |
|---|---|---|---|---|---|
| Offer letter | Employer | Yes, entirely | ATS or HRIS template | Generate it, or fill your own template | Free tier |
| I-9, Section 1 | Employee | Only as a “preparer” — Supplement A must be signed | Built in | Send a link for their half | Free (1 e-sign share) |
| I-9, Section 2 | Employer | Yes, after examining documents, within 3 business days | Built in | Filler + your own retention calendar | Free tier |
| Form W-4 | Employee | Identity fields only | Built in | Prefill, then send to finish | Free (1 e-sign share) |
| State withholding certificate | Employee | Identity fields only | Usually, if payroll runs there | A filler — this is the gap | $0–$39/mo |
| Direct deposit | Employee | No — you don't hold the details | Built in | Send a link | Free (1 e-sign share) |
| Benefits enrollment | Employee | No — elections are a choice | Carrier or broker portal | Carrier's PDF, prefilled then sent | $0–$39/mo |
| Policy acknowledgements | Employee signs | Identity block, never the signature | Built in | Filler with a signature link | Free (1 e-sign share) |
| Employment verification | Employer | Yes, entirely | Rarely — third-party PDFs | A filler — the other gap | $0–$39/mo |
One caveat on that cost column, because it decides whether the free route is real for you: Filly's free plan includes ten fills a month but only one e-sign share. Every row above that says “send a link” is free exactly once; routing signature requests as a habit starts at Solo, $19/month.
The half you are not allowed to prefill
Start with the I-9, the clearest case and the most expensive to get wrong. USCIS's instructions are unambiguous: the employee completes and signs Section 1 no later than their first day of employment, and may do it after accepting an offer but not before. The employer completes Section 2 within three business days of that first day.
Here is the part that catches teams who automate enthusiastically. USCIS defines a preparer and/or translator as any individual who helps the employee complete Section 1 — and that person must complete and sign a Certification on Supplement A. A workflow that prefills Section 1 for the employee has not removed a step; it has added one, and skipping it produces an I-9 that is wrong on its face.
The W-4 has the same shape with lower stakes: the identity block is data, the elections are the employee's decision and their signature attests to them. Benefits elections are a choice, not a record you hold. The pattern for all three is the boring one — fill the fields you legitimately own, then send the document out for the other party to finish and sign: the prefilled-form-to-sign workflow, and the only automation on these forms worth having. One duty no tool takes off you either: the completed I-9 must be kept for one year after employment ends or three years after the first day of employment, whichever is later. That is a calendar, not a document.
If you already pay for an HRIS, stop here
This section saves most readers a subscription. Payroll and HR platforms carry the federal onboarding forms natively, and a filler alongside one is waste.
- Gusto — self-onboarding emails the new hire so they e-sign their own paperwork, W-4s and I-9s included. Published monthly, no contract: Simple $49/mo + $6 per person/mo, Plus $80 + $12, Premium $180 + $22. One wrinkle: its onboarding material still puts custom document signing — offer letters, handbooks — on a “Complete plan,” a tier the current pricing page does not list, so confirm that feature sits on the tier you are quoted.
- BambooHR — new hires complete tax forms, I-9 verification and direct deposit before day one, with I-9 and E-Verify automated through a partner integration (Mitratech). Per employee per month: Core $10, Pro $17, Elite $25 for companies over 25 employees, or a flat rate from $250/mo at 25 employees or fewer. The page offers month-to-month or an extended term rather than a single billing cycle, so the term is part of the quote. E-signatures and the new-hire packet are in Pro and Elite, not Core.
- Rippling — generates new-hire paperwork for e-signature and tracks I-9 completion. It publishes no price: the pricing page is a quote form, and says most products bill per employee per month while some may be charged at or include a monthly base fee.
- Workday — enterprise HCM, equally quote-only. It does not publish HCM pricing anywhere: the HCM pages carry no dollar figures and route to Contact Sales.
The honest test: send an I-9 and a W-4 to a test employee from your HRIS. If it works, you do not have a form-filling problem. You have a training problem, which is cheaper.
What the ATS actually does — and doesn't
Greenhouse, Lever and Workable are hiring systems, and the document they own is the offer letter. Workable lists offer-letter templates among its recruiting features and e-signatures for company files on the HR side; Greenhouse lists e-signature across Core, Plus and Pro, priced by quote; Lever is quote-only too, onboarding sold as an add-on covering workflows, task management and document collection.
That is document generation: the layout is yours and the system merges a record into a template it controls. Right for an offer letter, useless against a state withholding certificate whose layout belongs to a revenue department that has never heard of your ATS. If fill-versus-generate is the question you are really trying to settle, the CRM, ATS and HR system comparison works through it tool by tool.
Workable is the only one of the three that publishes a price: Standard from $299/month for 1–20 employees, Premier $599, Enterprise $719. Read the toggle carefully — the annual figure beside Standard is $3,588, exactly twelve times the monthly price, under a label reading “save 20%.” Both cannot be true, so get the annual number in writing.
The forms that fall through the gap
Every stack leaks in the same places, and this is the only part of the lifecycle where a filler earns its keep: state withholding certificates (California's DE 4, New York's IT-2104 — if payroll does not run in that state yet, your HRIS does not carry the form); benefits carrier PDFs sent as flat files outside any portal; background-check authorisations on the vendor's own layout; employment-verification requests from a lender or landlord, due tomorrow and pure employer data; and contractor W-9s, not employment paperwork at all but landing in the same inbox. For the federal two, see the guides to filling Form I-9 and filling Form W-4.
With a developer, pdf-lib is MIT-licensed and free, and PDFtk Server is GPL v2 and free to use, with a $995 licence to redistribute it in a commercial product. Anvil hosts a template of your PDF and fills it over an API, metered at $0.10 per PDF fill or generation, with an AI Pack at $99/mo billed monthly ($79/mo billed yearly); its free plan covers dashboard and link submissions only, with metered usage switched off until you add a card, and its own page pairs that with a 2,500 starter-credit figure that reads inconsistently against it — so confirm credits against your account rather than the page.
For signature rather than filling, DocuSign lists Personal at $11/month with a 5-envelope-per-month limit, a figure shown on its annual basis ($132 committed for the year), and Dropbox Sign Essentials at $15/month for one user billed monthly.
Getting data out of the ATS without an integration
You do not need a live integration to stop retyping. Every ATS and HRIS exports a CSV, and one column per field is all a batch fill needs — the mechanics are in the batch-fill-from-a-spreadsheet guide. Cadence decides which you need, not sophistication: a cohort processed weekly is a CSV job and an integration for it is over-engineering, while a document that must exist seconds after a status flips to hired is an API job. Zapier and Make sit between — they move the record competently, but neither fills PDF form fields with its own native steps, which takes a third-party app such as PDF.co or PDF4me inside them, a second tool with its own bill.
Where Filly fits, and where it doesn't
Filly reads a form with AI, works out which field wants which detail, and fills it from a saved profile or a CSV, including scanned forms with no field layer. For the gap forms above that is the whole job, and the free plan covers 10 fills a month.
The limits, plainly, because they decide whether it suits you: no public API. No live CRM, ATS or HRIS integration. CSV only, not XLSX. A batch run is capped at 5 rows on Solo ($19/month) and 20 on Pro ($39/month), and there is no batch on the free plan at all. The free plan includes one e-sign share, not unlimited signature links. It is not a system of record, it does not run E-Verify — a Department of Homeland Security system you enrol in yourself, which no PDF tool owns — and it does not track I-9 retention deadlines. If your HRIS already sends I-9s and W-4s, do not buy this to sit next to it.
How to choose
- You have an HRIS: use it for I-9, W-4 and direct deposit. Add nothing.
- ATS but no HRIS: offer letters from the ATS; everything after the offer needs a second answer.
- Neither, under about ten hires a year: a filler on the free tier covers the filling, but the free plan's single e-sign share means routine signature links put you on Solo.
- Hiring in cohorts: CSV export plus batch fill, mindful of the row cap.
- A filled PDF the second a status changes: Anvil or your own code with pdf-lib. No no-code tool does this properly today.
Frequently asked questions
Can I prefill an employee's I-9 for them?
Not without becoming a preparer. Section 1 is the employee's attestation, and USCIS's instructions define anyone who helps them complete it as a preparer or translator, who must then sign the Certification on Supplement A. Prefilling without it produces a defective form. Prefill your own Section 2 instead, and send Section 1 to the employee.
Can Greenhouse or Lever fill a W-4?
No. They generate documents from templates they control — offer letters above all — and the W-4's layout belongs to the IRS. That is a job for an HRIS, or a PDF filler if you have no HRIS.
We hire in cohorts — can one run cover twenty people?
With Filly, a batch run is capped at 5 rows on Solo and 20 on Pro — twenty is one run on Pro, four on Solo, and the free plan has no batch at all. Above that the honest answers are an HRIS or an API. And a tool that runs a hundred rows at once is not automatically the right one: a hundred prefilled attestations nobody read is worse than four careful runs.
Do I need an integration, or is a CSV export enough?
Cadence decides it. If the paperwork is produced in weekly or per-cohort batches, a CSV export is enough and a live integration is over-engineering. If a filled PDF has to exist within seconds of a status change, that is an API job, and neither Filly nor a spreadsheet route will do it.
What happens when a state reissues its withholding form?
Field names move, and a hard-coded field map breaks silently — the fill still succeeds, the values land in the wrong boxes. That is the hidden running cost of the library route, and why most in-house scripts are eventually abandoned. A tool that reads the form each time absorbs the change; a map you wrote does not.
How current are these prices?
Checked against each vendor's own pricing page in August 2026, with the billing basis stated because that is where these comparisons go wrong. Gusto's figures are monthly, no contract. BambooHR's are per employee per month, on either month-to-month or an extended term. DocuSign's are annual-plan rates. Dropbox Sign's list prices carry promotional discounts on both cycles — a first-year discount on annual and a first-three-months discount on monthly — so the first invoice and the renewal differ. Workable's page shows an annual figure equal to twelve monthly payments under a “save 20%” label, which cannot be right as displayed. Rippling publishes no price at all, Workday publishes no HCM pricing, and Greenhouse and Lever are quote-only. Confirm against your own quote. This article is general information, not legal or HR compliance advice.