I have a couple of nice guitar midi files that I would like the scores for; is there any software out there that can do this sort of conversion, and output it as a PDF file?
Musescore is free as opposed to many other programs such as Sibelius or Finale. However, it is still very good and can do almost everything that paid programs can do.
One of the input files accepted in Musescore is MIDI and it can output PDF among other formats. However, as guidot said, it takes a human to do it right because a MIDI file does not contain all the information needed to create a complete score. Blanks, such as key signatures, time signatures, ornaments, articulations, and enharmonics, must be filled in by guessing.
That's where a human operator comes in. Your software, such as Musescore, must take the MIDI file and create a clean score with it. Musescore does a very good job at this, but the blanks in the MIDI file must be filled in by guessing. It takes a human operator to correctly fill these in, but having software to do the rough draft is helpful.
Once you have your software (such as Musescore), open the MIDI file. Musescore will convert the MIDI to sheet music, but you will still have to correct things (such as those mentioned above). If you have a good understanding of music, it shouldn't be too hard for most pieces. Once you've tidied the score up, output it as a PDF and you're done.
This is not quite a "conversion", since the midi file is on a much lower level than a score. So while you will surely get some output, it is more than questionable, whether somebody can play from it without considerable editing. As an example midi contains nothing about a key and so has to make wild guesses concerning accidentals, same for time signature, dotted notes, arpeggios may not be recognized as such but separate notes and many more issues. So I'm afraid to state, that there is nothing to replace human (here: a musicians) brain for that task.
As @guidot said, nothing replaces human oversight. But a good piece of software (I use Digital Performer, which is decidedly not free) can quantize the MIDI performance, which helps it render a more conventional-looking score. But you will still have to clean it up.
If you are looking for a free solution, Tuxguitar can help. It does have a midi input and a PDF output. It will work on windows, linux, and mac. However, you might have to do a bit of clean up; it won't know what key you are using or anything like that.
The free software Lilypond comes with a tool called
midi2ly, it converts
lilypond-files and lilypond outputs
pdf-files by default. But as many of the other answers already stated: "The real work starts when the conversion is done!"
I think many of the aspects are covered in the other answers but I'll show a quick example how a score can look like directly after a midi import:
$ midi2ly infile.midi -o outfile.ly
$ lilypond outfile.ly
And here is a the finished score, witch apart from:
needed to be completely remade.
Note: Lilypond is available for major distributions such as: Windows, Linux, macOS, FreeBSD a.o. but it does not come with a classical graphical user interface (GUI). Instead it is working on source files that can get created with a text editor and get compiled with the program more comparable to a
TeX/LaTeX workflow. There is editing software available such as Frescobaldi or software more gaining towards a GUI workflow such as Denemo.