1. Read the requirements as separate checks
Write down the required file type, maximum size, pixel dimensions, page count, and any photo or document rules. A file can pass one check and fail another: a 200x200 image can still be too large, and a small PDF can still have the wrong number of pages.
If the instructions are unclear, keep the original file. Do not guess at a crop, background color, page order, or compression level when the receiving organization has not stated what it accepts.
2. Prepare an image without losing the subject
Use crop-to-fill when the target must be completely covered and the outer edges can be removed. Use fit-with-background when the whole photo, logo, or scan must remain visible. Do not stretch a rectangular source into a square.
Resize to the required pixels first, then compress to the required KB or MB if necessary. Check the downloaded dimensions and file format after both steps.
3. Prepare a PDF without hiding quality problems
Compress only when the original exceeds the upload limit. Open the result and inspect signatures, stamps, tables, small text, and scanned pages before submitting it.
For forms, fill and flatten the document when the recipient needs a non-editable copy. Keep a separate original so you can correct a field without starting over.
4. Check the final file before uploading
Check the downloaded file itself, not only the settings shown by the tool. Confirm its name, extension, byte size, dimensions, page count, readability, and that it opens in a normal viewer.
For sensitive applications, browser-local processing keeps the selected file in the current tab. The website still loads application code and other page resources, so read the privacy explanation and use the privacy proof when you need to inspect the network behavior.