What's the file format of my object?

Most formats can be identified with their file name extension. You can find a list of file name extensions on Wikipedia.

If Windows is hiding the filename extensions, you can look them up by right-clicking on the file to see the file properties. 

For identifying an object without an extension it's possible to use the TrIDNet - File Identifier or a similar program.

Extensions can be ambiguous. Another method for finding out about the format is to check the metadata, if available.

For finding out about metadata, codecs or framerates of video-files, you can use the VLC Media Player. By klicking on the file's name in the play list additional information is shown.

For validating, if your PDF-file really meets PDF/A standards, the PDF Association published helpful guidelines on their web page: