What OFX is
OFX is the format behind the Download Transactions button on your bank's website. Version 1 is SGML, where a leaf element has an opening tag and no closing one. Version 2 is real XML. QFX is Intuit's variant of the same thing with a few extra tags, which is why a .qfx file opens in Quicken and is refused by software that only knows plain OFX.
Retail banks, credit card issuers and brokerages, because it is what Quicken and Microsoft Money asked for and the industry standardised on.
What PDF is
PDF describes a page: glyphs at coordinates, not rows and columns. A table in a PDF is a visual arrangement, not a data structure.
Reports, invoices, statements and anything sent to be read rather than processed.
What changes when you convert OFX to PDF
Each STMTTRN block becomes a row: date, amount, type, payee, memo, cheque number and the bank's own transaction id. The account number and currency come from the statement header and are added to every row, so a file merged with another still says which account it came from. Both the SGML and the XML flavour are read the same way.
The table is drawn into a paginated document with the header repeated on every page, so a long table stays readable past page one. Page size, orientation and font size are all adjustable.
What carries over from OFX to PDF
OFX records 4 things about a table that PDF has no way to hold.
OFX knows which of its values are numbers. PDF keeps only their appearance, so nothing downstream can sort or sum them without someone reading them back off the page first.
An empty cell and a missing one are the same thing in PDF, so a null and an empty string in the OFX both come out blank and can no longer be told apart.
OFX can hold a value that is itself a list or an object. PDF has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
PDF is the end of the line for this data. Reading the table back out of it is a separate and much harder problem than writing it, so keep the OFX if you will need the values again.