Expense systems want a document, not a camera roll. One PDF with all the receipts in it is usually what gets approved without questions.
Whoever approves your claim is checking the amount, the date and the merchant. If those three are crisp, a slightly creased or curled receipt is not a problem. If the total is blurred, the claim comes back.
Receipts on till paper are the hardest thing to photograph, because they curl and reflect. Flattening one under a book for a minute, or holding it flat, makes far more difference than any adjustment afterwards.
Keep the order matching your claim. An approver working through a list of items should find receipt three on page three, and anything else adds friction to something you want approved quickly.
Each photo becomes its own page, so one page per receipt keeps the file easy to check. Use the page that fits the photo exactly if you do not want white margins around a narrow receipt, and put the receipts in date order before you save, because the order cannot be changed afterwards.
Make the photos smaller first with Compress image if you have many, since each one is embedded as it is. Name the file with the month so you can find it later. The pages are pictures, so the PDF is not searchable.
Usually yes. It makes checking straightforward. Several small receipts on one page is acceptable if all the totals are legible.
Raise the contrast before converting. Till receipts fade quickly, so photograph them early.
No.
The PDF pages are pictures and are not searchable. Image to text can read the words from them into a separate text file.