Newbie

Again, without seeing the score, we can't really tell what's going on, so we can't really help.

That said, (unless you have changed the defaults!) when selected, Voice 1 notes and rests are blue; Voice 2 notes and rests are green, Voice 3 notes are reddish-brown, and Voice 4 notes are purple. What you want to try to do is to move the largest voice in a measure to Voice 1. Then manually add the notes from Voice 2 to Voice 1 (unless it's impossible! You may well end up with notes in more than one Voice!), then manually add the notes from Voice 3 and Voice 4 to Voice 1 (and, if necessary, Voice 2).

In the screenshot above, Voice 1 is all the notes with stems pointing up, and the C in the whole note interval. Voice 2 is all the notes with stems pointing down, and the A in the whole note interval.

I recommend you open a blank score and play with Voices 1 and 2 a little. You'll find that, when you enter notes into Voice 1 only, the stems will go up and down based on the position of the note on the staff. However, when you add notes to Voice 2, the stems on Voice 1 will automagically go up and the stems on Voice 2 will automagically go down. Experiment with this a little and you'll figure out the best way to combine the notes from your MIDI/PDF file (???) so that you can get them as neatly into as few voices as possible. If possible, you want all the notes in Voice 1. Only if it's required, do you want to put notes into Voice 2, then Voice 3, then Voice 4.

(That's the beginner aim. When you get better, there are occasions [very rare] when you might want to deliberately put notes into Voice 2 and not into Voice 1.)

For a bar that has too many beats, look at the Measure Properties (or Bar Properties if you have the UK version). Right-click on the measure (not on any note/rest, but on blank space within the measure) and click Measure Properties (or Bar Properties) from the context menu. Look at the "Measure duration" (or "Bar duration") and compare the "Nominal" versus the "Actual" values. If the extra beats are at the end and are all rests, you can just change the "Actual" to match the "Nominal". If there are notes on the extra beats, you will have to decide how to deal with them. One way is to add a new measure and move them into it ... but that might mean that you have half a measure. You might have to create a 2/4 measure in the middle of the 4/4 song; you might have to include an anacrusis (pickup notes) at the beginning and shift everything. Only you can tell what the best way to deal with these extra notes/beats.