Using multiple data items in foreach loop

You do not have the tools to solve your problem as it stands right now. Your methods GetCoAuthorsBetweenYears and GetVenuesBetweenYears simply do not return the necessary information.

Why? Well, how do you relate any given record returned by GetCoAuthorsBetweenYears to a Paper_Id? This method simply returns all CoAuthors stored in eAuthors. What you need is a method with one of the following signatures:

 List<Tuple<int, int>> GetDocumentsAndCoAuthorsBetweenYears(int lower, int upper) //Tuple.Value1 stores Paper_Id and Tuple.Value2 stores CoAuthor_ID.

 List<int> GetCoAuthorsByDocumentBetweenYears(int documentId, int lower, int upper)

Now, in both cases you can relate CoAuthor_ID information with Paper_IDs. Same with venues.

Ok, but if you can modify these methods, then why are we doing this to begin with? What prevents you from implementing the following one:

IEnumerable<PaperInfo> GetPaperInfoBetweenYears(int lower, int upper);

Where PaperInfo would be:

class PaperInfo
{
    public int Paper_ID { get; set; }
    public int CoAuthor_ID { get; set; }
    public int Paper_Category { get; set; }
    public int Venue_ID { get; set; }
}

And now you'd simply print your IEnumerable<PaperInfo>:

var papers = GetAllPaperInfoBetweenYears(year, year + 1);
var printedInfo = string.Join(Environment.NewLine,
                             papers.Select(p => string.Format("{0} {1} {2} {3}", p.Paper_ID, p.Paper_Category, p.CoAuthor_ID, p.Venue_ID));

UPDATE Per your comments, I've put together a small example:

 public class Author
 {
     public int Paper_ID { get; set; }
     public int CoAuthor_ID { get; set; }
     public int Venue_ID { get; set; }
     public int Paper_Category { get; set; }
     public int Year { get; }
     public int Publisher_ID { get; }
     //etc.
 }

 //bring all info from database   
 IEnumerable<Author> eAuthors = GetAllInfoFromDB();

 //Now filter and project what you need
 public static IEnumerable<PaperInfo> GetGetPaperInfoBetweenYears(this List<Author> eAuthors, int lower, int upper)
 {
     return from eAuthor in eAuthors
            where (eAuthor.Year >= lower && eAuthor.Year < upper)
            select new PaperInfo() { Paper_ID = eAuthor.Paper_ID, CoAuthor_ID = eAuthor.CoAuthor_ID, Paper_Category = eAuthor.Paper_Category, Venue_ID = eAuthor.Venue_ID };
 }

Of course you could even do without PaperInfo and simply filter by year and project the whole information stored in eAuthorInfo:

public static IEnumerable<PaperInfo> GetGetPaperInfoBetweenYears(this List<Author> eAuthors, int lower, int upper)
 {
     return from eAuthor in eAuthors
            where (eAuthor.Year >= lower && eAuthor.Year < upper)
            select eAuthor;
 }

And, same as before, simply print out the info you need:

var printedInfo = string.Join(Environment.NewLine,
                             papers.Select(p => string.Format("{0} {1} {2} {3}", p.Paper_ID, p.Paper_Category, p.CoAuthor_ID, p.Venue_ID)); //no year, publisher, etc. info

This is the way I'd do it, projections are really useful but are a pain when you have a lot of them and you can't use anonymous types; it makes you have to implement a type for each projection.