Sooner or later everyone needs to turn a HEIC photo into a JPG, a Word doc into a PDF, or a video into something a friend’s old phone can play. The web is full of “free converter” sites, and many are ad-choked or privacy-hostile. Here is how to convert common file types cleanly, safely, and usually without any website at all.
Documents: you probably do not need a website
For Word/Excel/PowerPoint to PDF, skip the converters entirely: every version of Microsoft Office and the free LibreOffice exports to PDF directly (File → Export / Save as PDF), and so does Google Docs. On any Mac or Windows machine you can also “print to PDF” from any app. These built-in routes preserve formatting far better than a random upload, and nothing leaves your device.
Images: HEIC, PNG, WebP
iPhone HEIC photos that will not open on Windows are the classic pain. On Windows, install the free HEIF extension from the Microsoft Store and Photos opens them natively. To batch-convert, the free open-source IrfanView (Windows) or XnConvert (all platforms) will turn hundreds of HEIC or PNG files into JPG or WebP in one pass, with control over quality. For a single quick job, macOS Preview and Windows Paint both “Save as” another format.
Audio and video: handbrake and VLC
For video, HandBrake (free, open-source) is the tool professionals and hobbyists alike reach for — it converts almost anything to a widely compatible MP4/H.264 with sensible presets like “Fast 1080p30.” VLC media player also converts audio and video via its Convert/Save menu. Both run entirely on your computer, so even large files are fast and private.
When a website is fine — and when it is not
Online converters are convenient for a one-off, small, non-sensitive file. Reputable ones like CloudConvert are transparent about handling and delete files after a while. But avoid uploading anything confidential — contracts, IDs, medical files — to any converter site, and be wary of sites that bury the convert button under fake download ads. The rule of thumb: if a good offline tool exists (and for the jobs above, it does), use it.
Lossy and lossless, and why the difference is permanent
Every conversion falls into one of two categories, and knowing which one you are performing prevents most conversion regret.
A lossless conversion preserves all the original information. PNG to BMP, FLAC to WAV, or a straight container change all belong here: the file size and format change, the underlying data does not. You can convert back and forth indefinitely without degradation.
A lossy conversion discards information permanently to save space. JPEG, MP3 and most video codecs work this way, and the discarded detail cannot be recovered by converting back. Converting a JPEG to PNG does not restore the detail the JPEG threw away; it simply stores the already-degraded image in a format that will not degrade it further.
Generation loss, the thing that ruins files quietly
Each lossy re-encode compounds on the last. Open a JPEG, make a small edit, save it, repeat a dozen times, and the result is visibly worse than the original even though no single step looked destructive. The artefacts accumulate around edges and in areas of subtle gradient.
The working habit that prevents this is to keep a master in a lossless format and export lossy copies for distribution. Edit the master, never the export. If you must work from a lossy file, minimise the number of save cycles and do all your edits in one session rather than repeatedly opening and resaving.
Choosing a target format
For photographs destined for the web, JPEG remains a reasonable default and WebP typically achieves similar quality at a smaller size. For images with sharp edges, flat colour or transparency, such as logos, screenshots and diagrams, PNG is the better choice because JPEG's compression produces visible halos around hard edges. For anything that must scale, a vector format such as SVG avoids the question entirely by storing shapes rather than pixels.
For documents that others must read exactly as laid out, PDF is the safe target. For documents that others must edit, sending a PDF is an obstacle rather than a courtesy.
Before you upload to an online converter
Web-based converters are convenient and appropriate for files you would be comfortable publishing. They are a poor choice for contracts, identity documents, medical records or anything containing other people's personal data, because the file is transmitted to and processed on a third-party server whose retention policy you have probably not read.
For sensitive material, convert locally with software on your own machine. The result is identical and the file never leaves your control.
Common questions
How do I convert a Word document to PDF for free?
Use the built-in export: Microsoft Office, free LibreOffice, and Google Docs all save directly to PDF, preserving formatting better than upload sites.
How do I open or convert iPhone HEIC photos on Windows?
Install the free HEIF extension from the Microsoft Store to open them, or batch-convert to JPG with free tools like IrfanView or XnConvert.
What is the best free video converter?
HandBrake — it is free, open-source, and converts almost any video to a compatible MP4 with easy presets, all offline for speed and privacy.
Are online file converters safe?
For small, non-sensitive files, reputable ones like CloudConvert are fine. Never upload confidential documents; use an offline tool for those.