Document
PDFPortable Document Format
PDF is a cross-platform document format created by Adobe in 1993. It preserves fonts, layout, images and vector graphics exactly the same on every device, which is why it became the default format for contracts, invoices, resumes and government forms.
Best for
Sending documents that must look identical for everyone — contracts, academic papers, printable forms, read-only exports.
Not for
Editing. PDFs are intentionally hard to modify. If you need to edit text, convert to Word first.
Document
DOCXMicrosoft Word Open XML Document
DOCX is the modern Word document format introduced in Office 2007. It's a ZIP archive containing XML files that describe the document's text, formatting and embedded media. Google Docs, Apple Pages and LibreOffice all read and write it.
Best for
Any document you need to edit — resumes, letters, reports, drafts shared with collaborators.
Not for
Final distribution. Different versions of Word render DOCX slightly differently. Export to PDF before sending.
Image
JPGJPEG — Joint Photographic Experts Group
JPG is a lossy photo compression format standardised in 1992. It drops imperceptible detail to shrink file size dramatically, which made digital photography practical. Every camera, phone, browser and app supports it.
Best for
Photos of real-world scenes — people, landscapes, products. The universal fallback when you don't know what format to use.
Not for
Logos, screenshots or anything with sharp edges and text. JPG smears them. Use PNG or WebP instead. Also no transparency.
Image
PNGPortable Network Graphics
PNG is a lossless image format created in 1996 as a free alternative to GIF. Unlike JPG, it saves every pixel exactly as given — nothing is thrown away — and it supports transparency. The trade-off is bigger files.
Best for
Screenshots, logos, icons, UI mockups, any graphic with text or sharp lines, and anything that needs a transparent background.
Not for
Photographs. PNG keeps photos at pristine quality but produces files 5–10× larger than an equivalent JPG.
Image
WebPWeb Picture format
WebP is a modern image format Google released in 2010. It supports both lossy (like JPG) and lossless (like PNG) compression, plus transparency and animation, in files 25–80% smaller than the format it's replacing. Every current browser supports it.
Best for
Images on websites. Smaller files mean faster page loads, which Google rewards in search rankings via Core Web Vitals.
Not for
Sending to someone's email or sharing in a chat app. Not every image viewer or legacy app opens WebP — convert to JPG first for maximum compatibility.
Image
HEICHigh Efficiency Image Container
HEIC is Apple's default photo format on iPhones since iOS 11 (2017). It uses HEVC compression to halve storage size compared to JPG at identical quality. The downside: Windows, Android and most web services don't open it natively.
Best for
Storing photos on an iPhone or Mac without filling up storage.
Not for
Sharing anywhere outside Apple's ecosystem. Convert to JPG first to guarantee the recipient can open it.
Audio/Video
MP4MPEG-4 Part 14 container
MP4 is a container format that holds video, audio, subtitles and metadata in one file. It's the de facto standard for streaming, YouTube, phone recordings and camera output. The video inside is usually H.264 or H.265.
Best for
Any video you want to play, upload or share. If a service accepts video, it accepts MP4.
Not for
Audio-only storage. If you only need the sound (lectures, interviews, podcasts), extract the audio to MP3 to save ~90% of the file size.
Audio/Video
MP3MPEG-1 Audio Layer III
MP3 is a lossy audio compression format standardised in 1993. It became the format that made digital music portable — the Walkman replacement, the iPod, the ringtone. Every media player on every platform supports it.
Best for
Music, podcasts, audiobooks, voice memos. Any audio you want playable everywhere.
Not for
Audio you'll re-edit professionally. Studios use lossless formats (WAV, FLAC) because re-encoding MP3 compounds quality loss.
