Often a digital source will reflow and present different pagination depending on the dimensions and resolution of the screen it's being viewed on, or the size of the text. Some documents will paginate differently when opened with different software. Some born-digital sources will not have pagination indicated at all. It is still important to be able to indicate exactly where in a document a quote or cited concept occurs. 

The Chicago Manual of Style provides useful guidance on this topic, in "14.160: Page or location numbers in electronic formats." CMOS suggests citing chapter numbers and/or section headings to get close to the specific point referenced.

APA goes a step beyond Chicago, encouraging us to locate exact paragraphs for notes. (See the section titled "Sources Without Page Numbers" in "In-Text Citations: Author/Authors" at Purdue OWL, or pp. 170-71 in the Publication Manual of the American Psychological Association.)  If the document itself does not number its paragraphs, APA suggests we count paragraphs following section headings to pinpoint the source cited. The parenthetical above would be constructed as an in-text citation as follows: (Purdue OWL, APA Formatting and Style Guide, Electronic Sources section, para. 5). 

MLA, on the other hand, prefers that writers never count paragraphs or assign them numbers. Instead, the citation should reference the nearest division that the source material itself makes -- chapter, section, or heading. See the MLA Handbook, 8th edition, p. 56. 

For all these styles, page numbers (in this case, exact locations in text) are necessary only for in-text citations or footnotes/endnotes.

Example

Citing this text from the charter of the United Nations (https://www.un.org/en/sections/un-charter/un-charter-full-text/):

"The International Court of Justice shall be the principal judicial organ of the United Nations. It shall function in accordance with the annexed Statute, which is based upon the Statute of the Permanent Court of International Justice and forms an integral part of the present Charter."

APA

(Charter of the United Nations, chapter XIV, article 92)

Chicago

1. Charter of the United Nations (June 26, 1945), chapter XIV, ¶ 1, https://www.un.org/en/sections/un-charter/un-charter-full-text/.

MLA

(Charter of the United Nations, chapter XIV)