Start with the task you need to finish
Use the file conversion guides to understand PDF, Word and Excel exports. Use the calculator guides to check the meaning of a percentage, discount, age, unit conversion or mortgage estimate. Each guide links back to the working tool and describes the result in practical terms.
What these guides do not do
They are not a replacement for a lender, tax authority, doctor, lawyer, accountant or the software that owns your source file. They are written to help you use a free utility carefully and recognize when the answer needs further confirmation.
Privacy is part of the explanation
The current file converter and most calculators operate in the browser on your device. The guide for each tool explains what is read, what is produced and which information the tool cannot preserve.
A checklist for better answers
If you are unsure which calculator fits your question or how much confidence to place in a result, start with the calculator checklist. It covers inputs, units, assumptions, simple cross-checks and when an official or professional source should take over.