If the honest answer is WhatsApp and a spreadsheet…

…your real competition is free, and the pitch here is organisation, not features. Here's a straight comparison — including where a spreadsheet genuinely does the job.

Spreadsheet + WhatsApp Generic CRM KaryaDocs
Client sees exactly what's missing
manual
not built for it
Document expiry tracking
No-login client upload link
varies
Per-party checklist fan-out
Who-viewed-this-file audit trail
varies
Configured for your vertical
manual setup
generic
WhatsApp as a real, tracked channel
it is WhatsApp — no record

To be fair to the free option: a spreadsheet can absolutely hold a list of clients and documents. What it can't do automatically or safely is fan a checklist out per party, flag an expiring document before it lapses, or answer "who viewed this file" — and WhatsApp genuinely is a real channel, it just keeps no record a firm can hand a client or an auditor.