Is there a way to combine multiple parts of a downloaded movie into one big file?

You could do that using Wundows Movie Maker

*Windows

for Apple-Users: iMovie.

www.freemake.com = download Freemake,

Much easier than Windows Movie Maker. and open source freeware.

Agreed with @RareDenver, use WMM. It’s super user-friendly and free.

And botches quality!

I assume you just want to watch all parts without further action. Media players like Gom player automatically play the next file – dependent on name.

Ex if Movie name 1.avi is followed by Movie name 2.avi it’ll automatically pre-load and play it in sequence. Also works with tv shows, you can play whole seasons, so long the files are named in a similar style.