10 guides · Using Our Tools
Using Our Tools guides
Walk-throughs for the calculators, converters, and utilities on this site — when to use which, with examples and common mistakes.
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Using Our Tools
How to merge PDFs
A simple, privacy-safe way to merge PDFs right in your browser. No watermarks, no sign-up, no upload. Takes under a minute.
Using Our Tools
How to split a PDF
Split a PDF by pages or ranges without uploading to a server. Clear steps, common pitfalls, and a free in-browser tool.
Using Our Tools
How to generate QR codes
Make a QR code for a URL, wifi, vCard, or plain text. What error-correction means, how big to print, how to test it.
More using our tools guides
How to calculate an age gap
A step-by-step method — and a free calculator — for finding the exact age gap between two people in years, months, and days.
How to calculate percentages
Percent of a number, percent change, percent off, markup, tip — the five most useful percentage formulas, with examples.
How to add a watermark to a PDF
Stamp a text watermark across every page of a PDF. When to use DRAFT vs CONFIDENTIAL, opacity tips, and a free tool.
How to add page numbers to a PDF
Add page numbers to any PDF — pick position, size, format. Why booklets need different numbering than contracts.
How to remove metadata from a PDF
PDFs carry author names, timestamps, and software traces you may not want to share. How to find it — and how to strip it.
How to Make a Simple Invoice
A freelancer-friendly guide to writing a clean, professional invoice — what to include, how to price, and getting paid.
How to Calculate Profit Margin
Gross, operating, and net profit margin explained with worked examples — so you know which number to quote and why.
Explore other guide sections
Cross-linked, lightly opinionated, and all written to be useful in five minutes.
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- Money & Business34 guidesFewer spreadsheets, better decisions.
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