Used this for years with Nag Screen, but

Usually I'm renaming sequential files, where the Incremental Number option fits the job.
Not this one

1559 Books released, Publisher code = R### suffix p for Print , and e for eBook

899 PDFs, all individually named, according to my own system.

Standardised Story Naming
R####e – <Title> by <Author(s)>
or if needed
R####e – <Title> + <(Un)Titled 2nd Story> by <Author(s)>

Standardised Story Series Naming
R####e – <Series Name> – Series – Story <Number> = <Title> by <Author(s)>
Where
R####e = Official Publisher ID Code
<Any Text> = <> and content replaced with eBooks specific details, using “Proper Case” Format.
“Proper Case” Format = Lower Case With Capitalised First Letter Of Every Word (Notepad++ “Convert Case To …” Option).
<Series Name> = Usually taken from the first Story.
Series = Standard series indicator.
Story <Number> = Written Number designating series order of the Story.
= is used to more clearly divide My Series naming conventions from <Title>
<Title> = Official eBook Name as displayed on the cover.
+ is used to clearly indicate divide between <Title> and <(Un)Titled 2nd Story>.
<(Un)Titled 2nd Story> = Official 2nd Story Name, even if not displayed on the cover.
by = Only word starting with a small case, always precedes author(s)’s name(s).
<Author(s)> = Author(s) name(s) as displayed on cover.

The covers available online are tiny 190×340 Pixels, and are stored online By publisher ID code.
There are a few print only no longer sold gaps, in the eBook lists, but the codes were standardised via renaming, but just codes, it was enough.

"Calibre", a free eBook Management program, when configured correctly, will create cover.jpg files from the PDFs, 899 of them.
Using two other Free Tools "FreeCommander XE" file manager, and "LSE (Link Shell Extension)", a HardLink/SymLink/Junction creator.

So a Flat view of the files within Calibre's author Folder, gives me the 899 Cover.jpg files, but Explorer Copy/Move will only replace them, leaving one file.
LSE Hardlinks, as well as saving space, auto adds " - Hardlink" to first file conflict.

Subsequent file conflicts use " - Hardlink (#)" where # = # + 1 for each duplicate, as the first duplicate raised #=1, so first number seen is 2

Cover - Hardlink (2).jpg
…
Cover - Hardlink (898).jpg
Cover.jpg This was manually renamed to Cover - Hardlink (0).jpg
Cover - Hardlink.jpg This was manually renamed to Cover - Hardlink (1).jpg

Resulting in
Cover - Hardlink (0).jpg
…
Cover - Hardlink (898).jpg

So now I had my files sequentially in the right order, ready for renaming, but there's only 899, of a possible 1159 numbers, so lots of gaps spread throughout the sequence, and my previous techniques won't work, so what will.

Advanced Renamer Docs research to the rescue
A CSV file list, apparently, and as I read the docs, I realise, I can name match to the PDFs, and use my full names FTW.

A quick Copy of Filenames, using yet another useful free tool, "Lammer Context Menu", and one that even has some limited renaming ability, but I use for it's file path copying, something Explorer has lacked since forever, though W11 v21H2 added a very limited "Only in speech Marks" method recently.

Paste the names into my last must have free tool, Notepad++
You might get the idea I like that price tag, and I do, but in each case it's best tool for the job is also free.
Use the Search, and Replace function to rename ".PDF" to ";"
New Case All Caps (Extension) Selected
New Name <CSV:1> (Name) Selected, and go.

Time taken, with research =1 hour
Time taken, without needing research = 5 minutes
Time estimated to do all that manually minimum = 1 week.

I came here, to instantly buy a Personal License, after doing that, then wrote this.
I can live with the Nag screen, being on a very low income (UK Benefits), but this tool is worth every penny of the £20 price tag.