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Guides

Practical answers to the questions that come up when converting files.

Answers, not marketing

Most conversion advice online exists to get you to click a button. These guides exist because the button sometimes does not help, and knowing why saves more time than trying another tool. They cover the questions that come up repeatedly: a PDF that refuses to shrink no matter what you do, the choice between three image formats that each claim to be best, and a photo format your own computer will not open.

Each guide is written to be useful whether or not you use our tools. Where a tool genuinely solves the problem, it is linked. Where it does not — and that happens, compression cannot rescue a scanned document — the guide says so and points at what actually works instead.

Why these three

They are the questions behind most conversion attempts that end in frustration. PDF size because the word "compress" implies a guarantee the format cannot always keep, and the reason is invisible until you know what to look for. Image formats because the choice is usually made by habit rather than by content, and the wrong habit either triples your page weight or covers your screenshots in artefacts. HEIC because millions of people meet it for the first time as an error message, with no indication of what the file even is.

All three share a theme worth stating once: file formats encode assumptions about their content. JPEG assumes a photograph, PNG assumes a graphic, HEIC assumes a modern decoder. Most conversion problems are really a mismatch between those assumptions and the file in front of you — which is why understanding the format beats trying another converter.

The tools these guides point to

Everything referenced here runs entirely in your browser. Files are read into memory, processed with JavaScript and handed straight back — nothing is uploaded, so there is no size cap beyond your device's memory and no queue to wait in.

For documents there are PDF tools covering splitting, merging, compression, rotation, page removal and conversion to Word or images. For pictures, the image converters handle JPG, PNG, WebP and HEIC along with compression and resizing. Beyond those sit a QR code generator and reader, unit converters for length, weight, temperature and data storage, fourteen text tools from a word counter to a regular expression tester, colour tools including a WCAG contrast checker, and a set of everyday calculators.

That local-processing design is also why these guides can be blunt about limitations. There is no upsell behind them: if compression will not shrink your scan, saying so costs us nothing and saves you an afternoon.

All Guides

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Why won't my PDF get smaller?

What compression can and cannot do — and what to try instead

 🎨

JPG, PNG or WebP?

Choosing an image format, and the rule that matters more

 🍎

What is HEIC?

Why iPhone photos won't open, and what conversion costs

Frequently Asked Questions

No. Every tool on OneConvert is free with no account, so there is nothing to upsell. That is why a guide can say plainly that compression will not rescue a scanned document, rather than steering you toward another button.
No. The guides explain the formats and the trade-offs, which apply whatever software you use. Where one of our tools genuinely solves the problem it is linked, and where it does not, the guide says what does.
Because these are the three questions that account for most conversions that end in frustration. A guide is added when a question comes up repeatedly and the honest answer is longer than a sentence, rather than to fill a page.
The PDF guide. The short answer is that compression removes structural overhead, not image data, so a document that is mostly scanned pages has almost nothing to give up. The guide explains how to tell which kind you have.
WebP in nearly all cases, with JPEG as the fallback for photographs and PNG for graphics that need transparency in older software. The image format guide covers the reasoning and the cases where the rule does not hold.