If you’re sent documents in ZIP form, you can sometimes use iOS’s Quick Look option to view the contents. For properly unpacking ZIP or RAR archives, though, use the free app iZip.
The iZip app shows you contents of a ZIP file, and lets you choose what to do with each file extracted.
2. Creative File Formats
Photoshop PSD files can only be opened by Adobe’s Photoshop Touch app if they come through its Creative Cloud service. Use the free PSD Viewer for Photoshop to open these files on iOS. For Illustrator AI files, grab the free doctape viewer app, which is a cloud service that actually converts the file to a PDF for easy viewing. For InDesign INDD files, there are a couple of apps that rely on InDesign’s built-in preview image to enable you to view files: the free ADOView and the paid-for SneakPeek ($9.99).
To view EPS files, you can use doctape viewer again. For SVG files, use the free Inkpad app. For DWG CAD files, you can use the free AutoCAD 360 app to view and edit the files, or use the paid CAD View 3D app ($4.99) by Afanche Technologies to view more CAD file types. ATView3D Professional ($19.99) from the same developer is compatible with a wide range of 3D app file types. For Rhino 3DM files, use the paid iRhino 3D app ($3.99).
PSD Viewer is highly responsive for viewing your Photoshop documents.
3. Image File Formats
While Apple’s iPhoto app is capable of opening many raw photo file types using the iTunes File Transfer feature, it can’t open them directly from the iPad. You need an app called PhotoRaw ($9.99 — there’s a Lite version too), which can open a huge range of raw file formats, perform basic edits, and export to JPEG.
iOS doesn’t support viewing GIF files natively when sent in emails (though it does in Messages, oddly). Open them in Adobe Reader and you see the animation, though.
4. Audio/video File Formats
For FLAC, AmpliFLAC Free lets you listen to up to 120 seconds of a song without paying. Equalizer Pro ($2.99) lets you listen to both FLAC and OGG tracks. For MKV, WMV, and AVI files, use the free-but-basic VLC for iOS app, or the great AVPlayerHD ($2.99).