How to Send Sensitive Documents Safely
Contracts, payslips, tax returns, medical letters and ID copies should not travel as plain email attachments. Four steps — compress, watermark, password-protect, share the password separately — take a couple of minutes, and with FileSlim all of them run in your browser. The document is never uploaded to us, unlike most online PDF tools.
The four steps
1. Compress it
Shrink the PDF so it fits the email or portal limit.
Open Compress PDF for upload →2. Watermark ID copies
Stamp copies of passports, ID cards or payslips with their purpose, e.g. "Copy for rental application only – 30 Sep 2026". A copy marked this way is harder to reuse for anything else.
Open Watermark PDF →3. Add a password
Encrypt the PDF with AES-256 so only people with the password can open it.
Open Protect PDF →4. Send the password separately
Email the file, but share the password by phone, SMS or a messenger — never in the same email.
Why "no upload" matters here
Most free PDF websites process your file on their servers. For a holiday photo that may be fine; for a passport scan or an employment contract it means a copy exists on a machine you do not control. FileSlim tools use your browser's own processing, so the file stays on your device.
A password on a PDF protects it in transit and in inboxes. It is not a substitute for your employer's or bank's secure upload portal when one is offered — use that first.
Common questions
What if I forget the PDF password?
It cannot be recovered — FileSlim never sees or stores it. Keep the unprotected original on your own device.
Will the recipient need special software?
No. Any modern PDF reader — Adobe Acrobat, browser viewers, Apple Preview — asks for the password and opens the file.
Should I watermark before or after adding the password?
Before. Once encrypted, the PDF cannot be edited without the password, so compress and watermark first, then protect it last.