Numerous primary sources have been reproduced in print form to be sold and distributed. This increases access to a work - for example, a Renaissance woman's diary might lay undiscovered in an archives, but an historian might come along and decide that it is foundational, and should be made widely available. So, the diary is then printed as a book and multiple copies are sold. These printed editions differ from a scholarly historical monograph as they are still primary sources - the "raw data" that is used in the analysis found in historical monographs. Printed editions may be: diaries, treatises, midwife manuals, a script... things that were not necessarily created for wide distribution, but then are deemed important enough to print, bind, and sell.

Be aware that printed editions may be EDITED - they might be translated into English, they may only contain excerpts, or they may contain commentary or annotations. It is a primary source, but you are not looking at the original source - only a surrogate. It is always helpful to note in your analysis that you are using a modern edition, demonstrating that you are aware there might be errors. 

Searching for these can be tricky. Your best bet is to find a relevant primary source in your secondary sources (articles, books) and try a title search. If you wish to do a broad search or sweep, here are a few keyword tips:

• Using "renaissance" as a keyword might limit you - if the record does not specify it is renaissance-associated. A work might list a year range, or a person, or an event, but it might not actually say "renaissance." 
• More modern words like "gender" might not find you a primary source; you will often have to use words of the time.
• Try searching for a specific person, event, or object (etc.) in conjunction with the type of source you are trying to find. (DaVinci AND diaries)
• While not perfect, you can also change to Advanced Search. Then, on the first line, select the dropdown "Genre/Form," and enter the type of source you are looking for (diaries, correspondence, letters). Then in the following lines, enter keywords (DaVinci; plague). Below is an example:

You will find a couple of different types of printed editions. First, a full work, like a diary, or a healing manual. Second, a collection of smaller works, for example, a collection of letters by Italian women. Please review the following so that you can see the difference.

Modern printed edition:

Click on the link for this first one. You'll note that there is a diary author, and an editor. The description reads: "Diary discusses the expedition of Charles VIII, 1494-1496 in Italy." The record makes it clear that it is a single work by a single author written from 1494-1496, but was published by an editor in 1967.

Primary source collection:

Note that this is not a single letter, but a collection of letters. You could use one or more of the letters in this collection as your evidence, or in your argument and discussion. These are all by a single author, but some collections may have works by multiple authors, all gathered together under a theme. Be aware that collections of works are heavily edited - only some sources make it into the volume, and do not reflect the entirety of the archive.