When writing a dissertation, scientific article, or conducting research, it’s vital to know how to use citation systems. The citation system can differ depending on your school of research and other factors. As such, we’ll discuss how you use the APA, MLA, and Chicago in-text citation format and how you should write the author reference citation. At the end of our article, you should be able to cite any PDF source in your paper without problems.

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What Are Text Citations and When Are They Needed

Citation is critical for any professional paper, especially when presenting your research or writing a scientific article. It’s also a key aspect of any dissertation, thesis, master’s, or other graded document. Basically, if you’re presenting the paper or article to any professional community, then you must cite your sources in-text, giving credit where credit is due is vital. Plagiarism is a surefire way to get your research scrapped or not taken seriously in the professional community, so you must source any research and ideas that aren’t yours. 

As such, you must use a citation format when using original concepts of a person. Citation is a way to add a reference to the author in your article or paper and acknowledge that’s where you obtained the information. There are different styles of citation, depending on the field you’re working in.

PDFs are becoming more popular, and where, in the past, you’d have cited books and physical research articles, it’s now largely swapped over to citing PDFs. Most research and scientific articles are published as PDFs, as it lasts longer, are available online, and are easier to access. As such, it’s critical to know how to cite a PDF document.

Further, when you cite a PDF file, there’s often a DOI (Digital Object Identifier), which serves as the unique webpage. Generally, you’ll reference it in the following format: https://doi.org/xx.xxxx/xxx.xxxx.xxxx. However, it can differ depending on the citation format you use in the article.

Some PDFs are just a file format to show another type of source. For example, you can find a newspaper article saved as a PDF. In that case, you must cite the source as a newspaper article. However, no matter how you cite it, you should include the URL or DOI to identify that it’s a PDF instead of a physical newspaper.

Different In-Text Citation Structures and Styles

Many citation format styles use in-text citations to add an author reference citation. The reason is that it doesn’t disrupt the article or paper’s flow. It’s a way to create minimal distractions so that the reader can focus on the core of the article but still have access to your sources that prove your research is credible.

It also means it’s easy enough to add your sources as you work and has the reader know which information is from which sources. This referencing makes it easy for any professional to verify your facts or even to read more about a particular theory of information nugget you dropped in your paper.

As we mentioned before, there are different structures when citing your sources. You must know these structures, as a small mistake in your source format can lead to ridicule from the professional society or even accusations of plagiarism. Below, we’ll explore the three most common structures: The APA style, the MLA system, and the Chicago format.

APA Style

You generally use the APA format in the social sciences, like the criminal justice, psychology, and education fields. You’ll find this format requires a comma between the author reference citation and the publication year when you use an in-text citation.

When adding your author reference citation list at the end of your document, there should be more information, like the URL, DOI, and the full source name. There are two ways you can cite in-text citations in the APA format, namely in prose and parenthetical. We explore both options below.

Citation in Prose

You should use this style if you use the author’s name in your article, as the only information you must further provide for the in-text citation is the publication date. See the example below on how you should cite in prose during your article.

Kellogg (2007) argues that cognitive psychology and cognitive science strongly influence how we scientifically understand psychology and the human mind.

As you can see, this format is quite simple and very easy to use.

Parenthetical Citation

Another way to use it is in a parenthetical citation, where you don’t mention the author’s name in the text. You often use it when you borrow a direct quote from the document, and you should add the author’s last name and the publication year in the parenthesis at the end of the quote.

“Cognitive psychology and its more inclusive partner, cognitive science, exert a strong influence on psychology as a whole and promise a scientific understanding of the human mind in all its complexity and significance” (Kellogg, 2007).

Note how there’s a comma between the author’s surname and the publication date and how the full stop is after the parenthesis ends.


APA uses a Reference list entry page to show all your sources. It requires a title and a page number in the document’s running head. Further, you use sentence case for headings with the APA format, which means you capitalize the first word and the proper nouns, but nothing else.

Below, we look at how you should write a reference in APA format in the Reference list.

  • Kellogg, R.T. (2007). Fundamentals of cognitive psychology. Sage Publications, Inc. https://books.google.co.za/books?id=0amWkgs7pQoC&printsec=frontcover&dq=psychology&hl =en&sa=X&redir_esc=y#v=onepage&q=psychology&f=false

As seen above, the author reference citation first says the surname, followed by the initials of his full name. The publication date should be in parentheses, followed by the book’s title in sentence case. Lastly, you write the publisher in italics at the end of the reference.

MLA Style

You’ll find that professionals in the humanities field, which includes languages, biology, and philosophy, prefer the MLA format. Unlike APA, the MLA format doesn’t use PDF identifiers or dates for a dateless article. Instead, you’re encouraged to use the file’s DOI, as it’s a permanent factor unique to the document.

When you use the citation in-text, you provide the author’s last name and the page number. Like APA, you can cite in prose or parenthetical, both of which we explore below.

Citation in Prose

As stated previously, when you cite in prose, it means you use the author’s surname in your text. However, instead of the publication date like with APA, you’ll add the book page where the author mentioned the information.

Heilbroner states in his philosophy of technology that it’s not possible to advance our society and technology without first experiencing the prerequisite stages, so if you want to know how to use the steam mill, you must first experience the hand mill (336).

Note that, unlike APA, the page number isn’t placed directly behind the author’s surname but rather at the end of the information provided by this author on this page.

Parenthetical Citation

In parenthetical citation, you either don’t use the author’s name in the text or quote something they said directly from the source. In that case, you cite as below.

“To put it differently, I believe that it is impossible to proceed to the age of the steam mill until one has passed through the age of the hand mill…” (Heilbroner 336).

Notice that the MLA format doesn’t add a comma between the author reference and the page number, but you should still place the full stop after the parenthesis. 

Works Cited

Unlike the APA Reference listings, the MLA format has a “Works Cited” page. Unlike APA, you don’t require a page title, and you include your last name and page number in the running head section. Here, you must provide more information about your sources, like the title, publisher, and date published.

We provide an example below for your reference.

  • Heilbroner, Robert L. “Do Machines Make History?” Technology and Culture, vol. 8, no. 3, 1967, pp. 335–45. https://doi.org/10.2307/3101719 

See that in this example, the title is in quotation marks, and you capitalized each major word. It’s also a good idea to add the DOI if you have it, as it’s a unique link to the source.

Also, should you be using an extract of the original book, as was done in this example where The Johns Hopkins University Press published a section of the book, you place the publication title in the quotation marks. You then list the original source in italics instead of the publisher. 

However, let’s imagine that the extracted section is the book, and The Johns Hopkins University Press is the original publisher. Then a standard MLA reference looks like this:

  • Heilbroner, Robert L. “Do Machines Make History?” The Johns Hopkins University Press, 1967. https://doi.org/10.2307/3101719 

Chicago Style

The Chicago format is more present in the subject of fine art and history, as compared to the other two styles. It also uses the author-date system or the bibliography system instead of parenthetical or in prose citations. The purpose of these systems is to guide the reader through the text with numbered notes or references in parentheses. 

Below, we look at how to cite using the two format styles.

Notes and Bibliography

In-text citations become streamlined using this format, as it uses the numbered footnotes system. Each raised superscript number corresponds with a numbered footnote at the bottom of the page for easy access. See the below example of how the Chicago format note style works.

As Joy Hakim says, “There’s a whole lot more to this freedom story, but the thing to keep in mind is that we started a way of governing that speaks to the whole world.”²

Once you’ve added this to your text, you’ll have to add the footnote in the bibliography that corresponds to it, like the below example.

2. Hakim, Joy. Freedom: A History of US. PDF File. 2003. https://books.google.co.za/books?id=xrtjr5MuyPQC&printsec=frontcover&dq=history+us&hl=en&sa=X&ved= 2ahUKEwjvi5zJ0pT9AhV8SUEAHQZICCEQ6AF6BAgGEAI#v=onepage&q=history%20us&f=false 

As you can see, the author’s name follows her surname. After that, you have the italicized title, and then the PDF identifier follows, which is crucial in the Chicago format.

Author-Date System

For the author-date system, you briefly cite a source using parenthesis, similar to the APA style. Like the note style, you must match the reference with the bibliography. Below is an example of how we’d use this style.

As Joy Hakim says, “There’s a whole lot more to this freedom story, but the thing to keep in mind is that we started a way of governing that speaks to the whole world” (Hakim, 2003).

Note that the full stop comes after the parenthesis and that there’s a comma between the author’s surname and the publication date. The bibliography will then contain a reference that gives you more information, like:

  • Hakim, Joy. Freedom: A History of US. PDF File. 2003. https://books.google.co.za/books?id=xrtjr5MuyPQC&printsec=frontcover&dq=history+us&hl=en&sa=X&ved= 2ahUKEwjvi5zJ0pT9AhV8SUEAHQZICCEQ6AF6BAgGEAI#v=onepage&q=history%20us&f=false

As this is the bibliography, not the footnotes, you don’t need to start the reference with a number. Otherwise, this style of referencing is the same as the footnote format. 

Final Thoughts

Citation in a scientific article or research paper is crucial to avoid plagiarism. There’s nothing wrong with using others’ theories and research to support your own, but you must give them credit. Using a site like the PDFplatform app lets you easily add an in-text citation to a PDF document without needing to access the original editable file. Check out the PDFplatform today to make citation easy.