Micrography (from Greek, literally small-writing – "Μικρογραφία"), also called microcalligraphy, is a Jewish form of calligrams developed in the 9th century, with parallels in Christianity and Islam, utilizing minute Hebrew letters to form representational, geometric and abstract designs.(From the Wikipedia page on micrography ).
The original suggestion may have arisen because Bacon was seen as the 'great wonder-worker' and researcher of scientific knowledge of his time, which had led in his lifetime to controversy and his being condemned as a heretic. The document has, in the late 20th century, been shown to physically date to more than a century after Bacon’s death. (Analysis of the text to date it - such as with the Donation of Constantine  - only works if the text is capable of being understood, which does not apply in this case.)
Newbold came to the conclusion that the document had been written with micrography and a complex system of multiple levels of encoding and anagrams, to show that Bacon had developed many of the scientific concepts previously assigned to later periods.
However John Manly was to prove that much of what Newbold had seen was the accidental by-product of cracking of the ink and other physical changes in the manuscript, and that the stated process of creating anagrams involved too much ambiguity in decoding.
Even if “someone from the timeframe within which the manuscript was created and written" (whether or not making use of earlier information) is considered instead, there are further purely practical arguments against Newbold's thesis:
- the length of the document and the practicalities of so much encoding at various levels.
- whether the ink and writing implements then available allowed for writing on such a microscopic scale.
- why so many levels of encoding, given that there were well-established alchemical and allegorical substitutions and Caesar codes.
- to what extent could the worldviews at the time of writing encompass the range of ideas suggested.