Learn English – Is it proper to use capital letters in (e.g.) document names

If it's not a proper noun, don't capitalise (unless in a title, or the first word at the start of a sentence.)

For example, the Wikipedia impact assessment entry begins:

Impact assessment (IA) is "a process aimed at ...

Further, their acronym and initialism entry says:

The expansion is typically given at the first occurrence of the acronym within a given text, for the benefit of those readers who do not know what it stands for. The capitalization of the original term is independent of it being acronymized, being lowercase for a term such as frequently asked questions (FAQ) but uppercase for a proper name such as the United Nations (UN).

The Capitalisation of Nouns (closest modern parallel, German) faded away between the Middle and End of the Eighteenth Century. The Reason was primarily Æsthetic, as Writers and Printers moved away from Heavy Typography towards a more Italianate Model. There were also Œconomic Advantages, since it generally made Typesetting easier.

The heaviest Stiles of Typography are usually associated with low-status or popular Publications -- the Equivalent of today's Tabloids, with their shouty sans-serif Headlines. That fits with your cited Text -- the anti-coffee Pamphlet mentioned in Harper's this Month, which is fairly Shouty even by Restoration Standards.

By Contrast, high-status Writers (and their Printers) tended to favour lighter Typographical Stiles, especially going into the Augustan Age. (Alexander Pope is a good Example One who 'lightened' the Typography of his Books over the Course of his Career, particularly in Editions meant for Persons of Quality)

The Change didn't occur at once, by some top-down Decree, but happened over a long period of Time, and according to Fashion. Regular Nouns go from Capitalised to lower-case; emphasised Nouns go from Italicised-capitalised to italicised or roman lower-case, depending on House Stile. Certain proper Nouns go from Sᴍᴀʟʟ Cᴀᴘꜱ to Capitalised.

David Foxon's Pope and the Early Eighteenth-Century Book Trade is the canonical Work on this Topic.

As to when the rule of capitals for nouns was inherited into English, that perhaps can never be known.

Since German capitalizes every noun there is speculation that this rule has been inherited from there, perhaps via Johannes Gutenberg and his famous printing press via the Gutenberg Bible (note that the Gutenberg press is not the first of its kind as the Chinese and Koreans already had this technology as early as 1000s). This could be where the Germanic rule of capitalizing nouns may have originated since the Gutenberg (and subsequent presses) were all German in origin and their language and grammar rules may have influenced the rules of printed words far and wide.

Capitalized nouns were a common occurrence and can be seen in many instances prior to the 1730s and seems to be a shift at this point. From this first issue of the Gentleman's Magazine published in 1731. Every noun has been capitalized. This heavy use of capitals seems to be common especially in the printed word. David Foxon wrote in his book entitled Libertine literature in England, 1660-1745 that "... the vogue for heavy caps may be associated with the eighteenth-century culture of sensibility." Also, "Heavy caps also seem to be associated with the more chatty, conversational style of prose that comes into fashion in the late seventeenth and early eighteenth centuries."

There is a steady drop of capitalizing every noun as can be seen by this volume of the Gentleman's Magazine printed in 1744. This starts to look familiar with printed and accepted usage by today's standard.