What QIF is
QIF is a plain text list of transactions, one field per line, each line beginning with a single letter that says which field it is. D is the date, T the amount, P the payee. A caret on its own line ends a transaction.
Quicken, and the long tail of banks and budgeting apps that still offer it because everything can read it.
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 QIF to PDF
Each block up to a caret becomes a row. Split transactions, which QIF writes as repeated S, E and $ lines, are joined into single cells rather than being spread across as many columns as the most-split transaction in the file has parts. The account type from the !Type header is added as a column.
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 QIF to PDF
QIF records 3 things about a table that PDF has no way to hold.
QIF 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.
QIF can be read one record at a time. PDF has to be complete before it means anything, so the whole table is held in memory while it is written and a file that gets cut off part way through is not partly usable - it is unusable.
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 QIF if you will need the values again.