Citation Linker
Add links to the numbered citations of a PDF, such as [3]: each opens the DOI its reference prints or jumps to the reference. Free, in your browser.
About This Tool
Citation Linker adds links to the numbered citations of a PDF. It finds the list of references at the end of the document, reads its numbered entries, and then finds the citations in square brackets, such as [1], [2, 3] or [4–7], in the text before the list. A click on a citation then takes the reader to what it cites.
Every citation that was matched to an entry is listed first, with its page, the reference it cites and where its link will lead: to the DOI or the web address the reference prints, or to the reference itself, where it stands in the document. Untick the ones you do not want. Each link lies on the citation alone: on the whole of [1], and on each number of [2, 3] by itself. In a range such as [4–7] the first and the last number are linked, since the ones between are not written.
The list is recognised by its heading, such as References, Bibliography or Works Cited, in English, Arabic or Chinese, or without a heading by three numbered entries in a row. Its entries may be numbered [1], [2] or 1., 2.. Nothing is looked up online: an address is read from the reference as it is printed. The links are invisible, the text is not changed, and citations that already have a link are left as they are. Everything happens in your browser.
How to Use
Upload the PDF
Choose one PDF that has real text and a numbered list of references. The search starts by itself. If there is no such list, or no citation matches it, the page says so.
Look through what was found
Each citation is listed with its page, where its link will lead and the reference it cites. Untick a citation to leave it without a link. To make every link jump to its reference instead of opening a web address, untick "Open the DOI or web address a reference prints".
Add the links and download
Click the button that adds the links, then "Download". Open the result in the PDF reader you normally use and try a few of them.
Use Cases
Papers that cite with bracketed numbers
A reader of a paper that cites as [1], [2] can click a citation to see its reference, and click again in the reader to go back.
Checking your own manuscript
The list shows which citations were matched to an entry of your reference list. A citation that is missing from it has a number the list does not have.
A reading copy with working DOIs
Where the references print their DOIs, each citation opens the cited work in the browser with one click.
Frequently Asked Questions
Which citation styles does it recognise?
Numbers in square brackets: one, such as [1]; several, such as [2, 3] or [2; 3]; and ranges, such as [4-7] or [4–7], of which the first and last number are linked. The digits may be Arabic-Indic ones. Author and year citations such as (Smith, 2020), numbers in round brackets and raised numbers without brackets are not recognised, and a citation broken over two lines is missed.
How does it find the list of references?
By its heading: References, Reference List, Bibliography, Works Cited, Literature Cited, المراجع, المصادر or 参考文献, alone on its line, with or without a section number. If the document has several, the last one with numbered entries under it is used, so a document with a list for each chapter is linked to its last list only. Without a heading, three entries numbered 1, 2, 3 in a row are taken for the list. The entries must be numbered one after another from 1.
Does it look up DOIs online?
No. It reads the DOI or the web address printed in the reference and nothing is sent anywhere. A DOI that is cut by the end of a line is put together again when that can be told; a web address cut that way cannot be told from a complete one, so it is not used and the link jumps to the reference instead. Look at the addresses in the list before you add the links.
Will the links work in every PDF reader?
They are ordinary PDF links: one kind opens a web address, the other shows the reference inside the document, with its first line at the top of the window. If you add links to a file a second time, the citations that already have them are left out, so nothing is doubled.