Much depends on what you mean by "scan papers into." If we're dealing with photos, drawings and the like it's a very easy process with a scanner and any reasonable scanning software. These software packages allow you to make tonal/contrast/exposure adjustments before scanning and further adjustments afterwards. In addition, the scans can be transferred to "higher level" graphics packages for further processing.
If the task is getting TEXT into the machine, we run into another set of parameters. We can take a graphic "picture" of the text, just like the photos/drawings mentioned above. However, these are static representations of the text, (i.e. a picture) and can't easily be altered as "written word"
In order to achieve actual "written word" we use a scanner and OCR (optical character recognition) software that first takes a "picture" then matches the picture of each character to a letter. Good OCR is relatively difficult, and even with a very good package, the error rate is relatively high, so, unless you have access to ultra-professional level scanners and software, you'll need to be prepared to do a lot of proof reading and correction.
One 'good' this is that many of the error occur in a regular pattern. Once you've figured out that pattern, you can do a global search/replace to correct all of those pattern errors at once.
I've scanned various books for work related projects as well as scanning the horridly hand written and (ancient style) typewritten manuscript for a book my father in law was writing. He worked on it for 14 years. I converted it in about 4 weeks and he subsequently was able to finish the book in 6 more months. Believe me, modern methods make a HUGE difference!
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